Tag Archives: Quantum Physics

Sources of Low-Energy Events in Low-Threshold Dark Matter Detectors [CL]

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http://arxiv.org/abs/2011.13939


We discuss several low-energy backgrounds to sub-GeV dark matter searches, which arise from high-energy particles of cosmic or radioactive origin that interact with detector materials. We focus on Cherenkov radiation, transition radiation, and luminescence or phonons from electron-hole pair recombination, and show that these processes are an important source of backgrounds at both current and planned detectors. We perform detailed analyses of these backgrounds at several existing and proposed experiments. We find that a large fraction of the observed single-electron events in the SENSEI 2020 run originate from Cherenkov photons generated by high-energy events in the Skipper-CCD, and from recombination photons generated in a phosphorus-doped layer of the same instrument. In a SuperCDMS HVeV 2020 run, Cherenkov photons produced in the sensor holders likely explain the origin of most of the events containing 2 to 6 electrons. At SuperCDMS SNOLAB, Cherenkov radiation from radioactive contaminants in Cirlex could dominate the low-energy backgrounds. For EDELWEISS, Cherenkov or luminescence backgrounds are subdominant to their observed event rate, but could still limit the sensitivity of their future searches. We also point out that Cherenkov radiation, transition radiation, and recombination could be a significant source of backgrounds at future experiments aiming to detect dark-matter via scintillation or phonon signals. The implications of our results for sub-GeV dark-matter searches and for the design of future detectors are significant. In particular, several design strategies to mitigate these backgrounds can be implemented, such as minimizing non-conductive materials near the target, implementing active and passive shielding, and using multiple detectors. Finally, we speculate on the implications of our results for the development of quantum computers and neutrino detectors.

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P. Du, D. Egana-Ugrinovic, R. Essig, et. al.
Tue, 1 Dec 20
99/108

Comments: 30 pages, 21 figures, 4 appendices

Unruh-DeWitt Detector Differentiation of Black Holes and Exotic Compact Objects [CL]

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http://arxiv.org/abs/2011.10179


We study the response of a static Unruh-DeWitt detector outside an exotic compact object (ECO) with a general reflective boundary condition in 3+1 dimensions. The horizonless ECO, whose boundary is extremely close to the would-be event horizon, acts as a black hole mimicker. We find that the response rate is notably distinct from the black hole case, even when the ECO boundary is perfectly absorbing. For a (partially) reflective ECO boundary, we find resonance structures in the response rate that depend on the different locations of the ECO boundary and those of the detector. We provide a detailed analysis in connection with the ECO’s vacuum mode structure and transfer function.

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B. Holdom, R. Mann and C. Zhang
Mon, 23 Nov 20
21/63

Comments: 18 pages, 22 figures

Mid-infrared single photon detector with superconductor Mo$_{80}$Si$_{20}$ nanowire [CL]

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http://arxiv.org/abs/2011.06699


A mid-infrared single photon detector (MIR-SNSPD) was reported based on 30 nm-wide superconductor molybdenum silicide nanowires in this work. Saturated quantum efficiencies (QEs) were achieved at the wavelength ranging from 1.55 to 5.07 micrometer in experiments. At the same time, the intrinsic dark count rate (DCR) was below 100 cps. Thus, this device produced a noise equivalent power (NEP) of 4.5 * 10-19 W/sqrt(Hz). The results provide the foundation of developing 10 micrometer-SNSPD for the applications of infrared astronomy observation.

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Q. Chen, R. Ge, L. Zhang, et. al.
Mon, 16 Nov 20
20/57

Comments: N/A

Reply to "Comment on "Cosmic Microwave Background Constraints Cast a Shadow On Continuous Spontaneous Localization Models"" [CL]

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http://arxiv.org/abs/2010.04067


Our recent letter “Cosmic Microwave Background Constraints Cast a Shadow On Continuous Spontaneous Localization Models” has recently been criticised in [G. R. Bengochea, G. Leon, P. Pearle, and D. Sudarsky, arXiv:2006.05313 and arXiv:2008.05285]. In this reply, we explain why the arguments presented in those articles are either incorrect or a confirmation of the robustness of our results.

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J. Martin and V. Vennin
Fri, 9 Oct 20
37/64

Comments: 7 pages, 3 figures

Robust laboratory limits on a cosmological spatial gradient in the electromagnetic fine-structure constant from accelerometer experiments [CL]

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http://arxiv.org/abs/2010.01798


Quasar absorption spectral data indicate the presence of a spatial gradient in the electromagnetic fine-structure constant $\alpha$ on cosmological length scales. We point out that experiments with accelerometers, including torsion pendula and atom interferometers, can be used as sensitive probes of cosmological spatial gradients in the fundamental constants of nature, which give rise to equivalence-principle-violating forces on test masses. Using laboratory data from the Eöt-Wash experiment, we constrain spatial gradients in $\alpha$ along any direction to be $|\mathbf{\nabla} \alpha / \alpha| < 6.6 \times 10^{-4}~(\textrm{Glyr})^{-1}$ at $95\%$ confidence level. Our result represents an order of magnitude improvement over laboratory bounds from clock-based searches for a spatial gradient in $\alpha$ directed along the observed cosmological $\alpha$-dipole axis.

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Y. Stadnik
Tue, 6 Oct 2020
27/85

Comments: 7 pages

Highly-efficient generation of coherent light at 2128 nm via degenerate optical-parametric oscillation [CL]

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http://arxiv.org/abs/2008.07193


Cryogenic operation in conjunction with new test-mass materials promises to reduce the sensitivity limitations from thermal noise in gravitational-wave detectors. The currently most advanced materials under discussion are crystalline silicon as a substrate with amorphous silicon-based coatings. They require, however, operational wavelengths around 2 $\mathrm\mu$m to avoid laser absorption. Here, we present a light source at 2128 nm based on a degenerate optical parametric oscillator (DOPO) to convert light from a 1064 nm non-planar ring-oscillator (NPRO). We achieve an external conversion efficiency of ($88.3 \pm 1.4$) With our approach, light from the established and existing laser sources can be efficiently converted to the 2 $\mathrm\mu$m regime, while retaining the excellent stability properties.

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C. Darsow-Fromm, M. Schröder, J. Gurs, et. al.
Tue, 18 Aug 20
-983/70

Comments: To be published in Optics Letters

Mechanical Quantum Sensing in the Search for Dark Matter [CL]

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http://arxiv.org/abs/2008.06074


Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.

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D. Carney, G. Krnjaic, D. Moore, et. al.
Mon, 17 Aug 20
-1008/40

Comments: White paper/overview based on a workshop held at the Joint Quantum Institute, Maryland. 12 pages, 4 figures, table summarizing many experimental systems, 118 references

Exploring the landscape involving cosmic inflation and continuous spontaneous localization models [CL]

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http://arxiv.org/abs/2008.05285


In this work we consider a wide variety of alternatives opened when applying the continuous spontaneous localization (CSL) dynamical collapse theory to the inflationary era. This exploration includes: two different approaches to deal with quantum field theory and gravitation, the identification of the collapse-generating operator and the general nature and values of the parameters of the CSL theory. All the choices connected with these issues have the potential to dramatically alter the conclusions one can draw. We also argue that the incompatibilities found in a recent paper, between the CSL parameter values and the CMB observational data, are associated with specific choices made for the extrapolation to the cosmological context of the CSL theory (as it is known to work in non-relativistic laboratory situations) which do not represent the most natural ones.

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G. Bengochea, G. León, P. Pearle, et. al.
Fri, 14 Aug 20
-931/70

Comments: 13 pages

On the origin of entropy of gravitationally produced dark matter: the entanglement entropy [CL]

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http://arxiv.org/abs/2007.09196


We study the emergence of entropy in gravitational production of dark matter particles, ultra light scalars minimally coupled to gravity and heavier fermions, from inflation to radiation domination (RD). Initial conditions correspond to dark matter fields in their Bunch-Davies vacua during inflation. The out'' states are correlated particle-antiparticle pairs, and the distribution function is found in both cases. In the adiabatic regime the density matrix features rapid decoherence by dephasing from interference effects in the basis ofout” particle states, effectively reducing it to a diagonal form with a concomitant von Neumann entropy. We show that it is exactly the entanglement entropy obtained by tracing over one member of the correlated pairs. Remarkably, for both statistics the entanglement entropy is similar to the quantum kinetic entropy in terms of the distribution function with noteworthy differences stemming from pair correlations. The entropy and the kinetic fluid form of the energy momentum tensor all originate from decoherence of the density matrix. For ultra light scalar dark matter, the distribution function peaks at low momentum $\propto 1/k^3$ and the specific entropy is $\ll 1$. This is a hallmark of a \emph{condensed phase} but with vanishing field expectation value. For fermionic dark matter the distribution function is nearly thermal and the specific entropy is $\mathcal{O}(1)$ typical of a thermal species. We argue that the functional form of the entanglement entropy is quite general and applies to alternative production mechanisms such as parametric amplification during reheating.

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M. Rai and D. Boyanovsky
Wed, 22 Jul 20
-432/67

Comments: 54 pages

A comparison of g(1)(τ), g(3/2)(τ), and g(2)(τ), for radiation from harmonic oscillators in Brownian motion with coherent background [CL]

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http://arxiv.org/abs/2007.06470


We compare the field-field g(1)(\tau), intensity-field g(3/2)(\tau), and intensity-intensity g(2)(\tau) correlation functions for models that are of relevance in astrophysics. We obtain expressions for the general case of a chaotic radiation, where the amplitude is Rician based on a model with an ensemble of harmonic oscillators in Brownian motion. We obtain the signal to noise ratios for two methods of measurement. The intensity-field correlation function signal to noise ratio scales with the first power of |g(1)(\tau)|. This is in contrast with the well-established result of g(2)(\tau) which goes as the square of |g(1)(\tau)|.

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A. Siciak, L. Orozco, M. Fouché, et. al.
Tue, 14 Jul 20
-162/97

Comments: 23 pages, 2 figures, 3 Tables

Repeated radiation damage and thermal annealing of avalanche photodiodes [CL]

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http://arxiv.org/abs/2007.04902


Avalanche photodiodes (APDs) are well-suited for single-photon detection on quantum communication satellites as they are a mature technology with high detection efficiency without requiring cryogenic cooling. They are, however, prone to significantly increased thermal noise caused by in-orbit radiation damage. Previous work demonstrated that a one-time application of thermal annealing reduces radiation-damage-induced APD thermal noise. Here we examine the effect of cyclical proton irradiation and thermal annealing, emulating the realistic operating profile of a satellite in low-Earth-orbit over a two-year life span. We show that repeated thermal annealing is effective in maintaining thermal noise of silicon APDs within a range suitable for quantum key distribution throughout the nominal mission life, and beyond. We examine two strategies—annealing at a fixed period of time, and annealing only when the thermal noise exceeds a pre-defined limit—and find that the latter exhibits lower thermal noise at end-of-life for most samples. We also observe that afterpulsing probability of the detector increases with cumulative proton irradiation. This knowledge helps guide design and tasking decisions for future space-borne quantum communication applications.

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I. DSouza, J. Bourgoin, B. Higgins, et. al.
Fri, 10 Jul 20
-67/76

Comments: 7 pages, 8 figures

Bipartite temporal Bell inequalities for two-mode squeezed states [CL]

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http://arxiv.org/abs/2007.00458


Bipartite temporal Bell inequalities are similar to the usual Bell inequalities except that, instead of changing the direction of the polariser at each measurement, one changes the time at which the measurement is being performed. By doing so, one is able to test for realism and locality, but relying on position measurements only. This is particularly useful in experimental setups where the momentum direction cannot be probed (such as in cosmology for instance). We study these bipartite temporal Bell inequalities for continuous systems placed in two-mode squeezed states, and find some regions in parameter space where they are indeed violated. We highlight the role played by the rotation angle, which is one of the three parameters characterising a two-mode squeezed state (the other two being the squeezing amplitude and the squeezing angle). In single-time measurements, it only determines the overall phase of the wavefunction and can therefore be discarded, but in multiple-time measurements, its time dynamics becomes relevant and crucially determines when bipartite temporal Bell inequalities can be violated. Our study opens up the possibility of new experimental designs for the observation of Bell inequality violations.

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K. Ando and V. Vennin
Thu, 2 Jul 20
41/64

Comments: 17 pages without appendices (33 pages total), 8 figures

A three-wave mixing kinetic inductance traveling-wave amplifier with near-quantum-limited noise performance [CL]

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http://arxiv.org/abs/2007.00638


We present a theoretical model and experimental characterization of a microwave kinetic inductance traveling-wave amplifier (KIT), whose noise performance, measured by a shot noise thermometer, approaches the quantum limit. Biased with a dc current, the KIT operates in a three-wave mixing fashion, thereby reducing by several orders of magnitude the power of the microwave pump tone compared to conventional four-wave mixing KIT devices. It is built in an artificial transmission line intrinsically matched to 50 Ohms, whose dispersion allows for a controlled amplification bandwidth. We experimentally measure $17.6^{+1.1}_{-1.4}$ dB of gain across a 2 GHz bandwidth, with an input 1 dB compression power of -63 dBm within that bandwidth, in qualitative agreement with theory. Using the KIT as the first amplifier in an amplification chain, we measure a system-added noise of $0.61\pm0.08$ K between 3.5 and 5.5 GHz, about one eighth the noise obtained when using only a representative classical amplifier. The KIT contribution to this added noise is estimated to be $0.2\pm0.1$ K, consistent with the quantum limit on amplifier added noise. This device is therefore suitable to read large arrays of microwave kinetic inductance detectors or thousands of superconducting qubits.

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M. Malnou, M. Vissers, J. Wheeler, et. al.
Thu, 2 Jul 20
56/64

Comments: N/A

A room temperature optomechanical squeezer [CL]

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http://arxiv.org/abs/2006.14323


One of the noise sources that currently limits gravitational wave (GW) detectors comes from the quantum nature of the light causing uncertain amplitude and phase. Phase uncertainty limits the precision of an interferometric measurement. This measurement is also subject to quantum back-action, caused by the radiation pressure force fluctuations produced by the amplitude uncertainty (QRPN). In order to lower this quantum noise, GW detectors plan to use squeezed light injection. In this thesis, I focus on using radiation-pressure-mediated optomechanical (OM) interaction to generate squeezed light. Creating squeezed states by using OM interaction enables wavelength-independent squeezed light sources that may also be more compact and robust than traditionally used non-linear crystals. We analyze the system with realistic imperfections (losses & classical noise), and use the concepts to design an experiment to obtain the most possible squeezing in a broad audio-frequency band at room temperature. This involves an optimization for the optical properties of the cavity and the mechanical properties of the oscillator. We then show its experimental implementation, and subsequent observation of QRPN as well as OM squeezing. These are the first ever direct observations of a room temperature oscillator’s motion being overwhelmed by vacuum fluctuations. This is shown in the low frequency band, which is relevant to GW detectors, but poses its own technical challenges, and hence has not been done before. Being in the back-action dominated regime along with optimized optical properties has also enabled us to observe OM squeezing. That is the first direct observation of quantum noise suppression in a room temperature OM system. It is also the first direct evidence of quantum correlations in the audio frequency band, in a broad band at non-resonant frequencies.

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N. Aggarwal
Fri, 26 Jun 20
28/72

Comments: Ph.D. Thesis, MIT Physics, Jan 2019

The Geometrical Origin of Dark Energy [CL]

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http://arxiv.org/abs/2006.11935


The geometrical formulation of the quantum Hamilton-Jacobi theory shows that the quantum potential is never vanishing, so that it plays the role of intrinsic energy. Such a key property selects the Wheeler-DeWitt (WDW) quantum potential $Q[g_{jk}]$ as the natural candidate for the dark energy. This leads to the WDW Hamilton-Jacobi equation with a vanishing kinetic term, and with the identification $$ \Lambda=-\frac{\kappa^2}{\sqrt{\bar g}}Q[g_{jk}] \ . $$ This shows that the cosmological constant is a quantum correction of the Einstein tensor, reminiscent of the von Weizs\”acker correction to the kinetic term of the Thomas-Fermi theory. The quantum potential also defines the Madelung pressure tensor. Such a geometrical origin of the vacuum energy density, a strictly non-perturbative phenomenon, provides strong evidence that it is due to a graviton condensate. Time independence of the WDW wave-functional then would imply that the ratio between the Planck length and the Hubble radius is a time constant, providing an infrared/ultraviolet duality. This indicates that the structure of the Universe is crucial for a formulation of Quantum Gravity.

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A. Alon, E. Faraggi and M. Matone
Tue, 23 Jun 20
84/84

Comments: 13 pages

Black Hole Metamorphosis and Stabilization by Memory Burden [CL]

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http://arxiv.org/abs/2006.00011


Systems of enhanced memory capacity are subjected to a universal effect of memory burden, which suppresses their decay. In this paper, we study a prototype model to show that memory burden can be overcome by rewriting stored quantum information from one set of degrees of freedom to another one. However, due to a suppressed rate of rewriting, the evolution becomes extremely slow compared to the initial stage. Applied to black holes, this predicts a metamorphosis, including a drastic deviation from Hawking evaporation, at the latest after losing half of the mass. This raises a tantalizing question about the fate of a black hole. As two likely options, it can either become extremely long lived or decay via a new classical instability into gravitational lumps. The first option would open up a new window for small primordial black holes as viable dark matter candidates.

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G. Dvali, L. Eisemann, M. Michel, et. al.
Tue, 2 Jun 20
14/90

Comments: 34 pages, 8 figures, 1 appendix

How Gaussian can the Sky be? Primordial Non-Gaussianity from Quantum Information [CEA]

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http://arxiv.org/abs/2005.09506


Using the quantum information picture to describe the early universe as a time dependent quantum density matrix, with time playing the role of a stochastic variable, we compute the non-gaussian features in the distribution of primordial fluctuations. We use a quasi de Sitter model to compute the corresponding quantum Fisher information function as the second derivative of the relative entanglement entropy for the density matrix at two different times. We define the curvature fluctuations in terms of the time quantum estimator. Using standard quantum estimation theory we compute the non-gaussian features in the statistical distribution of primordial fluctuations. Our approach is model independent and only relies on the existence of a quasi de Sitter phase. We show that there are primordial non-gaussianities, both in the form of squeezed and equilateral shapes. The squeezed limit gives a value of $f_{\rm NL} \sim n_s-1$. In the equilateral limit we find that $f_{\rm NL} \sim 0.03$. The equilateral non-gaussianity is due to the non-linearity of Einstein’s equation. On the other hand, the squeezed one is due to the quantum nature of clock synchronization and thus real and cannot be gauged away as a global curvature. We identify a new effect: {\it clock bias} which is a pure quantum effect and introduces a bias in the spectral tilt and running of the power spectrum of order $\sim 10^{-4}$, which could be potentially measurable and yield precious information on the quantum nature of the early Universe.

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C. Gomez and R. Jimenez
Wed, 20 May 20
56/66

Comments: N/A

Emergence of classical behavior in the early universe [CL]

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http://arxiv.org/abs/2004.10684


We investigate three issues that have been discussed in the context of inflation: Fading of the importance of quantum non-commutativity; the phenomenon of quantum squeezing; and the ability to approximate the quantum state by a distribution function on the classical phase space. In the standard treatments, these features arise from properties of mode functions of quantum fields in (near) de Sitter space-time. Therefore, the three notions are often assumed to be essentially equivalent, representing different facets of the same phenomenon. We analyze them in general Friedmann-Lemaitre- Robertson-Walker space-times, through the lens of geometric structures on the classical phase space. The analysis shows that: (i) inflation does not play an essential role; classical behavior can emerge much more generally; (ii) the three notions are conceptually distinct; classicality can emerge in one sense but not in another; and, (iii) the third notion is realized in a surprisingly strong sense; there is exact equality between completely general $n$-point functions in the classical theory and those in the quantum theory, provided the quantum operators are Weyl ordered. These features arise already for linear cosmological perturbations by themselves: considerations such as mode-mode coupling, decoherence, and measurement theory –although important in their own right– are not needed for emergence of classical behavior in any of the three senses discussed. Generality of the results stems from the fact that they can be traced back to geometrical structures on the classical phase space, available in a wide class of systems. Therefore, this approach may also be useful in other contexts.

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A. Ashtekar, A. Corichi and A. Kesavan
Thu, 23 Apr 20
11/45

Comments: 38 pages; 3 Figures. The first and the last sections provide a succinct summary of the motivation results

Quantum sensing with milligram scale optomechanical systems [CL]

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http://arxiv.org/abs/2003.13906


Probing the boundary between classical and quantum mechanics has been one of the central themes in modern physics. Recently, experiments to precisely measure the force acting on milligram scale oscillators with optical cavities are attracting interest as promising tools to test quantum mechanics, decoherence mechanisms, and gravitational physics. In this paper, we review the present status of experiments using milligram scale optomechanical systems. We compare the feasibility of reaching the quantum regime with a pendulum, torsion pendulum, and optically levitated mirror. Considerations for designing a high $Q$ pendulum, condition for torsion pendulums to have better force sensitivity than pendulums, and constraints in designing optical levitation of a mirror are presented.

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Y. Michimura and K. Komori
Wed, 1 Apr 20
79/83

Comments: 14 pages, 6 figures

On the quantization of the extremal Reissner-Nordstrom black hole [CL]

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http://arxiv.org/abs/2003.07173


Following Rosen’s quantization rules, two of the Authors (CC and FF) recently described the Schwarzschild black hole (BH) formed after the gravitational collapse of a pressureless “star of dust” in terms of a “gravitational hydrogen atom”. Here we generalize this approach to the gravitational collapse of a charged object, namely, to the geometry of a Reissner-Nordstrom BH (RNBH) and calculate the gravitational potential, the Schr\”odinger equation and the exact solutions of the energy levels of the gravitational collapse. By using the concept of BH effective state, previously introduced by one of us (CC), we describe the quantum gravitational potential, the mass spectrum and the energy spectrum for the extremal RNBH. The area spectrum derived from the mass spectrum finds agreement with a previous result by Bekenstein. The stability of these solutions, described with the Majorana approach to the Archaic Universe scenario, show the existence of oscillatory regimes or exponential damping for the evolution of a small perturbation from a stable state.

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C. Corda, F. Feleppa and F. Tamburini
Tue, 17 Mar 20
2/63

Comments: 6 pages, submitted to Phys. Rev. D

Mixed State Dynamics with Non-Local Interactions [CEA]

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http://arxiv.org/abs/2002.09173


The evolution of degenerate matter out of equilibrium is a topic of interest in fields such as condensed matter, nuclear and atomic physics, and increasingly cosmology, including inflaton physics prior to reheating. This follow-up paper extends the recent paper on the super-de Broglie dynamics of pure condensates of non-relativistic identical particles subject to non-local two-body interactions to the dynamics of mixed states. It is found that the two-body correlation function plays an increasingly dynamical role in these systems, driving the development of condensates and distributed phases alike. Examples of distribution and correlation evolution are presented, including instances of collapse, bound and unbound states, and phonons in the bulk. Potential applications are also discussed.

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E. Lentz, L. Lettermann, T. Quinn, et. al.
Mon, 24 Feb 20
7/49

Comments: 6 pages, 3 figures

A systematic approach to realising quantum filters for high-precision measurements using network synthesis theory [CL]

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http://arxiv.org/abs/2002.07644


We develop a systematic approach to the realisation of active quantum filters directly from their frequency-domain transfer functions, utilising a set of techniques developed by the quantum control community. This opens the path to the development of new types of active quantum filters for high-precision measurements. As an illustration, the approach is applied to realise an all-optical unstable filter with broadband anomalous dispersion, proposed for enhancing the quantum-limited sensitivity of laser interferometric gravitational-wave detectors.

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J. Bentley, H. Nurdin, Y. Chen, et. al.
Wed, 19 Feb 20
15/62

Comments: N/A

Quantum sensor networks as exotic field telescopes for multi-messenger astronomy [IMA]

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http://arxiv.org/abs/2002.04352


Multi-messenger astronomy, the coordinated observation of different classes of signals originating from the same astrophysical event, provides a wealth of information about astrophysical processes with far-reaching implications. So far, the focus of multi-messenger astronomy has been the search for conventional signals from known fundamental forces and standard model particles, like gravitational waves (GW). In addition to these known effects, quantum sensor networks could be used to search for astrophysical signals predicted by beyond-standard-model (BSM) theories. Exotic bosonic fields are ubiquitous features of BSM theories and appear while seeking to understand the nature of dark matter and dark energy and solve the hierarchy and strong CP problems. We consider the case where high-energy astrophysical events could produce intense bursts of exotic low-mass fields (ELFs). We propose to expand the toolbox of multi-messenger astronomy to include networks of precision quantum sensors that by design are shielded from or insensitive to conventional standard-model physics signals. We estimate ELF signal amplitudes, delays, rates, and distances of GW sources to which global networks of atomic magnetometers and atomic clocks could be sensitive. We find that, indeed, such precision quantum sensor networks can function as ELF telescopes to detect signals from sources generating ELF bursts of sufficient intensity. Thus ELFs, if they exist, could act as additional messengers for astrophysical events.

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C. Dailey, C. Bradley, D. Kimball, et. al.
Wed, 12 Feb 20
54/58

Comments: 19 pages, 5 figures

Quantum correlations between the light and kilogram-mass mirrors of LIGO [CL]

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http://arxiv.org/abs/2002.01519


Measurement of minuscule forces and displacements with ever greater precision encounters a limit imposed by a pillar of quantum mechanics: the Heisenberg uncertainty principle. A limit to the precision with which the position of an object can be measured continuously is known as the standard quantum limit (SQL). When light is used as the probe, the SQL arises from the balance between the uncertainties of photon radiation pressure imposed on the object and of the photon number in the photoelectric detection. The only possibility surpassing the SQL is via correlations within the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light it reflects. Here, we experimentally prove the theoretical prediction that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitational-wave Observatory (LIGO). Our measurements show that the quantum mechanical uncertainties in the phases of the 200 kW laser beams and in the positions of the 40 kg mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty a factor of 1.4 (3dB) below the SQL. We anticipate that quantum correlations will not only improve gravitational wave (GW) observatories but all types of measurements in future.

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H. Yu, L. McCuller, M. Tse, et. al.
Thu, 6 Feb 20
25/57

Comments: N/A

Quantum nature of Wigner function for inflationary tensor perturbations [CL]

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http://arxiv.org/abs/2002.01064


We study the Winger function for the inflationary tensor perturbation defined in the real phase space. We compute explicitly the Wigner function including the contributions from the cubic self-interaction Hamintonian of tensor perturbations. Then we argue that it is no longer an appropriate description for the probability distribution in the sense that quantum nature allows negativity around vanishing phase variables. This comes from the non-Gaussian wavefunction in the mixed state as a result of the non-linear interaction between super- and sub-horizon modes. We also show that this is related to the explicit infrared divergence in the Wigner function, in contrast to the trace of the density matrix.

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J. Gong and M. Seo
Wed, 5 Feb 20
18/67

Comments: 24 pages

Second law of black hole thermodynamics [CL]

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http://arxiv.org/abs/2001.02897


If simple entropy in the Bekenstein-Hawking area law for a black hole is replaced with ‘negative’ quantum conditional entropy, which quantifies quantum entanglement, of positive-energy particles of the black hole relative to its outside, a paradox with the original pair-creation picture of Hawking radiation, the first law for black hole mechanics and quantum mechanics is resolved. However, there was no way to judge experimentally which area law is indeed adopted by black holes. Here, with the no-hair conjecture, we derive the perfect picture of a second law of black hole thermodynamics from the modified area law, rather than Bekenstein’s generalized one from the original area law. The second law is testable with an event horizon telescope, in contrast to Bekenstein’s. If this is confirmed, the modified area law is exalted to the first example of fundamental equations in physics which cannot be described without the concept of quantum information.

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K. Azuma and G. Kato
Fri, 10 Jan 20
40/65

Comments: 7 pages, 1 figure

Squeezing of primordial gravitational waves as quantum discord [CL]

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http://arxiv.org/abs/2001.02474


We investigate the squeezing of primordial gravitational waves(PGWs) in terms of quantum discord. We construct a classical state of PGWs without quantum discord and compare it with the Bunch-Davies vacuum. Then it is shown that the oscillatory behavior of the angular-power spectrum of the cosmic microwave background (CMB) fluctuations induced by PGWs can be the signature of the quantum discord of PGWs. In addition, we discuss quantum decoherence on the entanglement and the quantum discord of PGWs for super-horizon modes. For the state of PGWs with decoherence effect, we examine the decoherence condition and the correlation condition introduced by C. Kiefer et al. (Class. Quantum Grav. 24 (2007) 1699). We show that the decoherence condition is not sufficient for the separability of PGWs and the correlation condition implies the quantum discord of PGWs in the matter-dominated era.

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A. Matsumura and Y. Nambu
Thu, 9 Jan 20
53/61

Comments: 32 pages, 10 figures

Collapse models and cosmology [CL]

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http://arxiv.org/abs/1912.07429


Attempts to apply quantum collapse theories to Cosmology and cosmic inflation are reviewed. These attempts are motivated by the fact that the theory of cosmological perturbations of quantum-mechanical origin suffers from the single outcome problem, which is a modern incarnation of the quantum measurement problem, and that collapse models can provide a solution to these issues. Since inflationary predictions can be very accurately tested by cosmological data, this also leads to constraints on collapse models. These constraints are derived in the case of Continuous Spontaneous Localization (CSL) and are shown to be of unprecedented efficiency.

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J. Martin and V. Vennin
Tue, 17 Dec 19
9/89

Comments: 13 pages, 1 figure. Prepared for the volume “Do wave functions jump? Perspectives on the work of GC Ghirardi”, Editors: V. Allori, A. Bassi, D. D\”urr & N. Zangh`i; Springer International Publishing

Astro- and Quantum Physical Tests of Screened Scalar Fields [CL]

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http://arxiv.org/abs/1910.05738


In general, modified gravity theories are modifications or extensions of Einstein’s general relativity. Some of them give rise to additional scalar degrees of freedom in Nature. If these scalar fields exist and are light enough, they should cause a gravity-like fifth force that could, in principle, exceed gravity in its strength. However, there are tight constraints on fifth forces from Solar System-based tests. Screening mechanisms are popular means for avoiding these constraints by suppressing a fifth force in regions of high environmental mass density but allowing for phenomenologically interesting effects in environments of lower densities. In this thesis, scalar field models with screening mechanisms will be discussed and some astro- and quantum physical tests for their existence presented. At first, the impact of disformally coupled symmetrons on gravitational lensing by galaxies will be evaluated. Secondly, it will be shown how fluctuations of a chameleon scalar field induce the open dynamics of a quantum test particle. For this, tools from non-equilibrium quantum field theory will be introduced, developed and applied, and a quantum master equation derived.

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C. Käding
Thu, 12 Dec 19
11/58

Comments: PhD thesis; 140 pages

Precision frequency-comb terahertz spectroscopy on pure quantum states of a single molecular ion [CL]

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http://arxiv.org/abs/1911.12808


Spectroscopy is a powerful tool for studying molecules and is commonly performed on large thermal molecular ensembles that are perturbed by motional shifts and interactions with the environment and one another, resulting in convoluted spectra and limited resolution. Here, we use generally applicable quantum-logic techniques to prepare a trapped molecular ion in a single quantum state, drive terahertz rotational transitions with an optical frequency comb, and read out the final state non-destructively, leaving the molecule ready for further manipulation. We resolve rotational transitions to 11 significant digits and derive the rotational constant of CaH+ to be B_R = 142501777.9(1.7) kHz. Our approach suits a wide range of molecular ions, including polyatomics and species relevant for tests of fundamental physics, chemistry, and astrophysics.

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C. Chou, A. Collopy, C. Kurz, et. al.
Mon, 2 Dec 19
77/91

Comments: 25 pages, 4 figures, 6 tables

Cosmological Decoherence from Thermal Gravitons [CL]

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http://arxiv.org/abs/1911.10207


We study the effects of gravitationally-driven decoherence on tunneling processes associated with false vacuum decays, such as the Coleman–De~Luccia instanton. We compute the thermal graviton-induced decoherence rate for a wave function describing a perfect fluid of nonzero energy density in a finite region. When the effective cosmological constant is positive, the thermal graviton background sourced by a de Sitter horizon provides an unavoidable decoherence effect, which may have important consequences for tunneling processes in cosmological history. We discuss generalizations and consequences of this effect and comment on its observability and applications to black hole physics.

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N. Bao, A. Chatwin-Davies, J. Pollack, et. al.
Tue, 26 Nov 19
12/66

Comments: 30 pages, 6 figures; comments welcome

Restricted Boltzmann Machines for galaxy morphology classification with a quantum annealer [CL]

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http://arxiv.org/abs/1911.06259


We present the application of Restricted Boltzmann Machines (RBMs) to the task of astronomical image classification using a quantum annealer built by D-Wave Systems. Morphological analysis of galaxies provides critical information for studying their formation and evolution across cosmic time scales. We compress the images using principal component analysis to fit a representation on the quantum hardware. Then, we train RBMs with discriminative and generative algorithms, including contrastive divergence and hybrid generative-discriminative approaches. We compare these methods to Quantum Annealing (QA), Markov Chain Monte Carlo (MCMC) Gibbs Sampling, Simulated Annealing (SA) as well as machine learning algorithms like gradient boosted decision trees. We find that RBMs implemented on D-wave hardware perform well, and that they show some classification performance advantages on small datasets, but they don’t offer a broadly strategic advantage for this task. During this exploration, we analyzed the steps required for Boltzmann sampling with the D-Wave 2000Q, including a study of temperature estimation, and examined the impact of qubit noise by comparing and contrasting the original D-Wave 2000Q to the lower-noise version recently made available. While these analyses ultimately had minimal impact on the performance of the RBMs, we include them for reference.

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J. Caldeira, J. Job, S. Adachi, et. al.
Fri, 15 Nov 19
71/73

Comments: 13 pages; LaTeX; 11 figures

Dark energy as a large scale quantum gravitational phenomenon [CL]

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http://arxiv.org/abs/1911.02955


In our recently proposed quantum theory of gravity, the universe is made of `atoms’ of space-time-matter (STM). Planck scale foam is composed of STM atoms with Planck length as their associated Compton wave-length. The quantum dispersion and accompanying spontaneous localisation of these STM atoms amounts to a cancellation of the enormous curvature on the Planck length scale. However, an effective dark energy term arises in Einstein equations, of the order required by current observations on cosmological scales. This happens if we propose an extremely light particle having a mass of about $10^{-33} \ {\rm eV/c^2}$, forty-two orders of magnitude lighter than the proton. The holographic principle suggests there are about $10^{122}$ such particles in the observed universe. Their net effect on space-time geometry is equivalent to dark energy, this being a low energy quantum gravitational phenomenon. In this sense, the observed dark energy constitutes evidence for quantum gravity. We then invoke Dirac’s large number hypothesis to also propose a dark matter candidate having a mass halfway (on the logarithmic scale) between the proton and the dark energy particle, i.e. about $10^{-12}\ {\rm eV/c^2}$.

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T. Singh
Mon, 11 Nov 19
10/105

Comments: 9 pages

Probing Virtual Axion-Like Particles by Precision Phase Measurements [CL]

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http://arxiv.org/abs/1910.09973


We propose an experiment for detecting Axion-Like Particles (ALPs) based on the axion-photon interaction in the presence of a non-uniform magnetic field. The impact of virtual ALPs on the polarization of the photons inside a cavity is studied and a detection scheme is proposed. We find that the cavity normal modes are dispersed differently owing to their coupling to the ALPs in the presence of a background magnetic field. This birefringence, in turn, can be observed as a phase difference between the cavity polarization modes. The signal is considerably enhanced close to the resonance frequencies of the cavity and further enhanced for a squeezed light source. We propose to scan the resonances with a variable frequency source. We argue that the amplified signal allows for exclusion of a broad range of axion mass $10^{-3}\text{eV} \lesssim m_{a} \lesssim 1 \text{eV}$ even at very small axion-photon coupling constant with the potential to reach sensitivity to the QCD axion. Our scheme allows for the exclusion of a range of axion masses that has not yet been covered by other experimental techniques.

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M. Zarei, S. Shakeri, M. Abdi, et. al.
Wed, 23 Oct 19
26/64

Comments: 8 pages, 4 figures

Dispersion Properties, Nonlinear Waves and Birefringence in Classical Nonlinear Electrodynamics [CL]

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http://arxiv.org/abs/1910.08586


Using the very basic physics principles, we have studied the implications of quantum corrections to classical electrodynamics and the propagation of electromagnetic waves and pulses.
The initial nonlinear wave equation for the electromagnetic vector potential is solved perturbatively about the known exact plane wave solution in both the free vacuum case, as well as when a constant magnetic field is applied. A nonlinear wave equation with nonzero convective part for the (relatively) slowly varying amplitude of the first-order perturbation has been derived. This equation governs the propagation of electromagnetic waves with a reduced speed of light, where the reduction is roughly proportional to the intensity of the initial pumping plane wave. A system of coupled nonlinear wave equations for the two slowly varying amplitudes of the first-order perturbation, which describe the two polarization states, has been obtained for the case of constant magnetic field background.
Further, the slowly varying wave amplitude behavior is shown to be similar to that of a cnoidal wave, known to describe surface gravity waves in shallow water. It has been demonstrated that the two wave modes describing the two polarization states are independent, and they propagate at different wave frequencies. This effect is usually called nonlinear birefringence.

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S. Tzenov, K. Spohr and K. Tanaka
Tue, 22 Oct 19
56/91

Comments: 11 pages, 3 figures

Searching for scalar dark matter with compact mechanical resonators [IMA]

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http://arxiv.org/abs/1910.07574


We explore the viability of laboratory-scale mechanical resonators as detectors for ultralight scalar dark matter. The signal we investigate is an atomic strain due to modulation of the fine structure constant and the lepton mass at the Compton frequency of dark matter particles. The resulting stress can drive an elastic body with acoustic breathing modes, producing displacements that are accessible with opto- or electromechanical readout techniques. To address the unknown mass of dark matter particles (which determines their Compton frequency), we consider various resonator designs operating at kHz to MHz frequencies, corresponding to $10^{-12}-10^{-5}$ eV particle mass. Current resonant-mass gravitational wave detectors that have been repurposed as dark matter detectors weigh $\sim ! 10^3$ kg. We find that a large unexplored parameter space can be accessed with ultra-high-$Q$, cryogenically-cooled, cm-scale mechanical resonators possessing $\sim ! 10^7$ times smaller mass.

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J. Manley, R. Stump, D. Wilson, et. al.
Fri, 18 Oct 19
18/77

Comments: N/A

Graphene-based Josephson junction microwave bolometer [CL]

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http://arxiv.org/abs/1909.05413


Sensitive microwave detectors are critical instruments in radioastronomy, dark matter axion searches, and superconducting quantum information science. The conventional strategy towards higher-sensitivity bolometry is to nanofabricate an ever-smaller device to augment the thermal response. However, this direction is increasingly more difficult to obtain efficient photon coupling and maintain the material properties in a device with a large surface-to-volume ratio. Here we advance this concept to an ultimately thin bolometric sensor based on monolayer graphene. To utilize its minute electronic specific heat and thermal conductivity, we develop a superconductor-graphene-superconductor (SGS) Josephson junction bolometer embedded in a microwave resonator of resonant frequency 7.9 GHz with over 99\% coupling efficiency. From the dependence of the Josephson switching current on the operating temperature, charge density, input power, and frequency, we demonstrate a noise equivalent power (NEP) of 7 $\times 10^{-19}$ W/Hz$^{1/2}$, corresponding to an energy resolution of one single photon at 32 GHz and reaching the fundamental limit imposed by intrinsic thermal fluctuation at 0.19 K.

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G. Lee, D. Efetov, L. Ranzani, et. al.
Fri, 13 Sep 19
58/70

Comments: 8 pages, 4 figures

Oscillatory path integrals for radio astronomy [HEAP]

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http://arxiv.org/abs/1909.04632


We introduce a new method for evaluating the oscillatory integrals which describe natural interference patterns. As an illustrative example of contemporary interest, we consider astrophysical plasma lensing of coherent sources like pulsars and fast radio bursts in radioastronomy. Plasma lenses are known to occur near the source, in the interstellar medium, as well as in the solar wind and the earth’s ionosphere. Such lensing is strongest at long wavelengths hence it is generally important to go beyond geometric optics and into the full wave optics regime. Our computational method is a spinoff of new techniques two of us, and our collaborators, have developed for defining and performing Lorentzian path integrals. Cauchy’s theorem allows one to transform a computationally fragile and expensive, highly oscillatory integral into an exactly equivalent sum of absolutely and rapidly convergent integrals which can be evaluated in polynomial time. We require only that it is possible to analytically continue the lensing phase, expressed in the integrated coordinates, into the complex domain. We give a first-principles derivation of the Fresnel-Kirchhoff integral, starting from Feynman’s path integral for a massless particle in a refractive medium. We then demonstrate the effectiveness of our method by computing the interference patterns of Thom’s caustic catastrophes, both in their “normal forms” and within a variety of more realistic, local lens models, over all wavelengths. Our numerical method, implemented in a freely downloadable code, provides a fast, accurate tool for modeling interference patterns in radioastronomy and other fields of physics.

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J. Feldbrugge, U. Pen and N. Turok
Wed, 11 Sep 19
20/86

Comments: N/A

Photon vortex generation in quantum level by high-order harmonic synchrotron radiations from spiral moving electrons in magnetic fields [HEAP]

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http://arxiv.org/abs/1908.11545


We explore synchrotron radiations from a spiral moving electron under a uniform magnetic field along z-axis using Landau quantization. We found that this process generates a photon vortex with Bessel wave-function as the eigen-state of the z-component of the total angular momentum and the photon vortices with large angular momenta are generated by high-order harmonic radiations. We also calculate the decay widths and the energy spectra. Under strong magnetic fields as 10^13 G, which are found in astrophysical objects such as magnetars, photon vortices are predominantly generated.

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T. Maruyama, T. Hayakawa, T. Kajino, et. al.
Mon, 2 Sep 19
6/66

Comments: 12 pages, 4 figures

Photon vortex generation in quantum level by high-order harmonic synchrotron radiations from spiral moving electrons in magnetic fields [HEAP]

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http://arxiv.org/abs/1908.11545


We explore synchrotron radiations from a spiral moving electron under a uniform magnetic field along z-axis using Landau quantization. We found that this process generates a photon vortex with Bessel wave-function as the eigen-state of the z-component of the total angular momentum and the photon vortices with large angular momenta are generated by high-order harmonic radiations. We also calculate the decay widths and the energy spectra. Under strong magnetic fields as 10^13 G, which are found in astrophysical objects such as magnetars, photon vortices are predominantly generated.

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T. Maruyama, T. Hayakawa, T. Kajino, et. al.
Mon, 2 Sep 19
41/66

Comments: 12 pages, 4 figures

Entanglement and Collective Neutrino Oscillations [CL]

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http://arxiv.org/abs/1908.03511


We investigate the importance of going beyond the mean-field approximation in the dynamics of collective neutrino oscillations. Specifically, we use measures of nontrivial correlations (otherwise known as `entanglement’) between the constituent neutrinos of the many-body system, such as the entanglement entropy and the Bloch vector of the reduced density matrix. The relevance of going beyond the mean-field is demonstrated by comparisons between the evolution of the neutrino state in the many-body picture vs the mean-field limit, for different initial conditions.

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M. Cervia, A. Patwardhan, A. Balantekin, et. al.
Mon, 12 Aug 19
17/42

Comments: 17 pages of RevTeX, 9 figures

Testing fundamental physics with photon frequency shift [CL]

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http://arxiv.org/abs/1907.09542


We propose a high precision satellite experiment to further test Einstein’s General Relativity and constrain extended theories of gravity. We consider the frequency shift of a photon radially exchanged between two observers, one located on Earth and the other on a satellite in circular orbit in the equatorial plane. In General Relativity there exists a peculiar satellite-distance at which the static contribution to the frequency shift vanishes since the effects induced by pure gravity and special relativity compensate, while it can be non-zero in extended theories of gravity, like in models with screening mechanisms. As an experimental device placed on the satellite we choose a system of hydrogen atoms which can exhibit the $1$s spin-flip transition from the singlet (unaligned proton-electron spins) to the triplet (aligned proton-electron spins) state induced by the absorption of photons at $21.1$cm ($1420$MHz). The observation of an excited state would indicate that the frequency of the emitted and absorbed photon remains unchanged according to General Relativity predictions. On the contrary, a non-zero frequency shift, as predicted in extended theories of gravity, would prevent the spin-flip transition and the hydrogen atoms from jumping into the excited state. Such a detection would signify a smoking-gun signature of new physics beyond special and general relativity.

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L. Buoninfante, G. Lambiase and A. Stabile
Wed, 24 Jul 19
13/60

Comments: 7 pages, 2 figures, 2 tables

Structure Factors of The Unitary Gas Under Supernova Conditions [CL]

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http://arxiv.org/abs/1907.03914


We compute with lattice field theory the vector and axial static structure factors of the unitary gas for arbitrary temperature above the superfluid transition and for fugacities 0.1 < z < 1.0. Using the lattice formulation, we calculate beyond the validity of the virial expansion, a commonly used technique in many-body physics. We find qualitative differences in the behavior of the structure factors at high fugacity compared to the predictions of the virial expansion. Due to the large scattering length of neutrons, we expect the unitary gas structure factors to approximate the structure factors of hot neutron gases, and we therefore expect our calculations to be useful in supernova simulations, where neutron gas structure factors are needed to compute in-medium neutrino-neutron scattering rates.

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A. Alexandru, P. Bedaque and N. Warrington
Wed, 10 Jul 19
7/53

Comments: 10 pages, 6 figures, 1 table

SAGE: A Proposal for a Space Atomic Gravity Explorer [IMA]

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http://arxiv.org/abs/1907.03867


The proposed mission “Space Atomic Gravity Explorer” (SAGE) has the scientific objective to investigate gravitational waves, dark matter, and other fundamental aspects of gravity as well as the connection between gravitational physics and quantum physics using new quantum sensors, namely, optical atomic clocks and atom interferometers based on ultracold strontium atoms.

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G. Tino, A. Bassi, G. Bianco, et. al.
Wed, 10 Jul 19
16/53

Comments: Submitted to The European Physical Journal D for publication in the Topical Issue “Quantum Technologies for Gravitational Physics”

A cosmic shadow on CSL [CL]

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http://arxiv.org/abs/1906.04405


The Continuous Spontaneous Localisation (CSL) model solves the measurement problem of standard quantum mechanics, by coupling the mass density of a quantum system to a white-noise field. Since the mass density is not uniquely defined in general relativity, this model is ambiguous when applied to cosmology. We however show that some well-motivated choices of the density contrast already make current measurements of the cosmic microwave background incompatible with other laboratory experiments.

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J. Martin and V. Vennin
Wed, 12 Jun 19
27/59

Comments: 5 pages + appendix (13 pages total), 3 figures

Signatures of relic quantum nonequilibrium [CL]

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http://arxiv.org/abs/1906.03670


[Shortened Abstract:] This thesis explores the possibility that quantum probabilities arose thermodynamically. A chief concern is the detection of primordial quantum nonequilibrium', since this is observably distinct from textbook quantum physics. Chapters 2, 3, 4, and 5 are adaptations of references [1,2,3], and [4] respectively. <br />Chapter 2 proposes (information) entropy conservation as a minimal requirement for a theory to feature classical-style thermodynamic relaxation. The resulting structure is dubbedthe iRelax framework’. Both classical mechanics and de Broglie-Bohm quantum theory are shown to be special cases. Indications for a possible extension or unification of de Broglie-Bohm theory are briefly highlighted.
Chapter 3 examines ways in which quantum relaxation may be prevented. The method of the drift-field is introduced. A systematic treatment of nodes is given. A category of quantum states is found for which relaxation is significantly impeded, and may not complete at all.
Chapters 4 and 5 consider the possibility that primordial quantum nonequilibrium may be conserved in the statistics of a species of relic cosmological particle. Necessary factors for this to be the case are discussed and illustrative scenarios are given both in terms of nonequilibrium particles created by inflaton decay, as well as relic vacuum modes for species that decoupled close to the Planck temperature. The search for so-called `smoking-gun’ spectral lines created by dark matter decay or annihilation is argued to be a particularly promising setting for the detection of quantum nonequilibrium. Unintuitive spectral effects relating to the contextuality of quantum measurements are described. If such a suspected source of quantum nonequilibrium were found, its subjection to a specifically quantum mechanical test would confirm or deny the presence of the quantum nonequilibrium conclusively.

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N. Underwood
Tue, 11 Jun 19
40/60

Comments: PhD Thesis, 227 pages, 29 figures. Formatted for 6 x 9in paperback bookbinding. Draws heavily (with significant text overlap) on articles arXiv:1409.6817, arXiv:1609.04576, and arXiv:1705.06757

Resolving starlight: a quantum perspective [CL]

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http://arxiv.org/abs/1906.02064


The wave-particle duality of light introduces two fundamental problems to imaging, namely, the diffraction limit and the photon shot noise. Quantum information theory can tackle them both in one holistic formalism: model the light as a quantum object, consider any quantum measurement, and pick the one that gives the best statistics. While Helstrom pioneered the theory half a century ago and first applied it to incoherent imaging, it was not until recently that the approach offered a genuine surprise on the age-old topic by predicting a new class of superior imaging methods. For the resolution of two sub-Rayleigh sources, the new methods have been shown theoretically and experimentally to outperform direct imaging and approach the true quantum limits. Recent efforts to generalize the theory for an arbitrary number of sources suggest that, despite the existence of harsh quantum limits, the quantum-inspired methods can still offer significant improvements over direct imaging for subdiffraction objects, potentially benefiting many applications in astronomy as well as fluorescence microscopy.

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M. Tsang
Thu, 6 Jun 19
3/67

Comments: 21 pages, 7 figures. First draft of a review paper. Comments welcome

Axions and Atomic Clocks [CL]

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http://arxiv.org/abs/1905.10014


The equations of electrodynamics are altered in the presence of a classical coherent axion dark matter background field, changing the dispersion relation for electromagnetic waves. Careful measurements of the frequency stability in sensitive atomic clocks could in principle provide evidence for such a background for $f_a \ge 10^7$ GeV. Turning on a background magnetic field might enhance these effects in a controllable way, and interferometric measurements might also be useful for probing the time-varying photon dispersion relation that results from a coherent cosmic axion background.

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L. Krauss
Mon, 27 May 19
30/51

Comments: 3 pages, submitted to Phys. Rev. Lett

On the possibility of nonlinear de Broglie relations for very-high-energy photons [HEAP]

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http://arxiv.org/abs/1905.08206


While quantum field theory is at the heart of our understanding of a large variety of phenomena, there remains some discrepancies between theoretically predicted and observed quantities in the very-high-energy (VHE) domain. In this work, starting from commutation relations between phase-space operators (in “first quantization”) we define averaged creation and annihilation operators and show that they satisfy a simple, deformed commutation relation. By extending this relation to the quantized electromagnetic field, we are led to non-linear de Broglie relations for photons, which appreciably differ from $E=\hbar \omega$ and $\mathbf{p}=\hbar \mathbf{k}$ only in the VHE regime. The nonlinear Compton scattering that follows from these assumptions is discussed. We suggest that this hypothesis may be a way to deal with the pair-production anomaly and show that it may lead to an attenuation in the cosmological-constant problem of several orders of magnitude.

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F. Parisio
Tue, 21 May 19
15/71

Comments: N/A

Eigenvalues and eigenstates of the many-body collective neutrino oscillation problem [CL]

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http://arxiv.org/abs/1905.04386


We demonstrate a method to systematically obtain eigenvalues and eigenstates of a many-body Hamiltonian describing collective neutrino oscillations. The method is derived from the Richardson-Gaudin framework, which involves casting the eigenproblem as a set of coupled nonlinear “Bethe Ansatz equations”, the solutions of which can then be used to parametrize the eigenvalues and eigenvectors. The specific approach outlined in this paper consists of defining auxiliary variables that are related to the Bethe-Ansatz parameters, thereby transforming the Bethe-Ansatz equations into a different set of equations that are numerically better behaved and more tractable. We show that it is possible to express not only the eigenvalues, but also the eigenstates, directly in terms of these auxiliary variables without involving the Bethe Ansatz parameters themselves.

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A. Patwardhan, M. Cervia and A. Balantekin
Tue, 14 May 19
37/91

Comments: 17 pages of RevTeX, 4 figures

Quantum simulation of dark energy candidates [CL]

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http://arxiv.org/abs/1811.06927


Additional scalar fields from scalar-tensor, modified gravity or higher dimensional theories beyond general relativity may account for dark energy and the accelerating expansion of the Universe. These theories have lead to proposed models of screening mechanisms, such as chameleon and symmetron fields, to account for the tight experimental bounds on fifth-force searches. Cold atom systems have been very successfully used to constrain the parameters of these screening models, and may in future eliminate the interesting parameter space of some models entirely. In this paper, we show how to manipulate a Bose-Einstein condensate to simulate the effect of any screened scalar field model coupled conformally to the metric. We give explicit expressions for the simulation of various common models. This result may be useful for investigating the computationally challenging evolution of particles on a screened scalar field background, as well as for testing the metrology scheme of an upcoming detector proposal.

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D. Hartley, C. Käding, R. Howl, et. al.
Tue, 14 May 19
55/91

Comments: 26 pages, 3 figures

Quantum interference between light sources separated by 150 million kilometers [CL]

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http://arxiv.org/abs/1905.02868


We report an experiment to test quantum interference, entanglement and nonlocality using two dissimilar photon sources, the Sun and a semiconductor quantum dot on the Earth, which are separated by 150 million kilometers. By making the otherwise vastly distinct photons indistinguishable all degrees of freedom, we observe time-resolved two-photon quantum interference with a raw visibility of 0.796(17), well above the 0.5 classical limit, providing the first evidence of quantum nature of thermal light. Further, using the photons with no common history, we demonstrate post-selected two-photon entanglement with a state fidelity of 0.826(24), and a violation of Bell’s inequality by 2.20(6).

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Y. Deng, H. Wang, X. Ding, et. al.
Thu, 9 May 19
32/59

Comments: 16 pages, 5 figures

In search of an observational quantum signature of the primordial perturbations in slow-roll and ultra slow-roll inflation [CL]

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http://arxiv.org/abs/1905.01394


In the standard inflationary paradigm, cosmological density perturbations are generated as quantum fluctuations in the early Universe, but then undergo a quantum-to-classical transition. A key role in this transition is played by squeezing of the quantum state, which is a result of the strong suppression of the decaying mode component of the perturbations. Motivated by ever improving measurements of the cosmological perturbations, we ask whether there are scenarios where this decaying mode is nevertheless still observable in the late Universe, ideally leading to a “smoking gun” signature of the quantum nature of the perturbations. We address this question by evolving the quantum state of the perturbations from inflation into the post-inflationary Universe. After recovering the standard result that in slow-roll (SR) inflation the decaying mode is indeed hopelessly suppressed by the time the perturbations are observed (by $\sim 115$ orders of magnitude), we turn to ultra slow-roll (USR) inflation, a scenario in which the usual decaying mode actually grows on super-horizon scales. Despite this drastic difference in the behavior of the mode functions, we find also in USR that the late-Universe decaying mode amplitude is dramatically suppressed, in fact by the same $\sim 115$ orders of magnitude. We finally explain that this large suppression is a general result that holds beyond the SR and USR scenarios considered and follows from a modified version of Heisenberg’s uncertainty principle and the observed amplitude of the primordial power spectrum. The classical behavior of the perturbations is thus closely related to the classical behavior of macroscopic objects drawing an analogy with the position of a massive particle, the curvature perturbations today have an enormous effective mass of order $m_{\rm pl}^2/H_0^2 \sim 10^{120}$, making them highly classical.

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R. Putter and O. Doré
Wed, 8 May 19
35/48

Comments: 27 pages, 7 figures. Comments welcome

Linking multipole vectors and pseudoentropies for CMB analysis [CEA]

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http://arxiv.org/abs/1905.01176


Multipole vectors and pseudoentropies provide powerful tools for a numerically fast and vivid investigation of possible statistically anisotropic, respectively non-Gaussian signs in CMB temperature fluctuations. After reviewing and linking these two conceptions we compare their application to data analysis using the Planck 2015 NILC full sky map.

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M. Pinkwart, P. Schupp and D. Schwarz
Mon, 6 May 19
29/58

Comments: 6 pages, 1 figure; Prepared for submission to “Proceedings of the 15th Marcel Grossmann Meeting (Rome, July 1-7, 2018)”

On symmetries of Hamiltonians describing systems with arbitrary spins [CL]

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http://arxiv.org/abs/1905.00082


We consider systems where dynamical variables are the generators of the SU(2) group. A subset of these Hamiltonians is exactly solvable using the Bethe ansatz techniques. We show that Bethe ansatz equations are equivalent to polynomial relationships between the operator invariants, or equivalently, between eigenvalues of those invariants.

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M. Cervia, A. Patwardhan and A. Balantekin
Thu, 2 May 19
37/45

Comments: 8 Pages of LATEX; Dedicated to the memory of E. Henley

Vacuum Decay in Real Time and Imaginary Time Formalisms [CL]

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http://arxiv.org/abs/1904.08565


We analyze vacuum tunneling in quantum field theory in a general formalism by using the Wigner representation. In the standard instanton formalism, one usually approximates the initial false vacuum state by an eigenstate of the field operator, imposes Dirichlet boundary conditions on the initial field value, and evolves in imaginary time. This approach does not have an obvious physical interpretation. However, an alternative approach does have a physical interpretation: in quantum field theory, tunneling can happen via classical dynamics, seeded by initial quantum fluctuations in both the field and its momentum conjugate, which was recently implemented in Ref. [1]. We show that the Wigner representation is a useful framework to calculate and understand the relationship between these two approaches. We find there are two, related, saddle point approximations for the path integral of the tunneling process: one corresponds to the instanton solution in imaginary time and the other one corresponds to classical dynamics from initial quantum fluctuations in real time. The classical approximation for the dynamics of the latter process is justified only in a system with many degrees of freedom, as can appear in field theory due to high occupancy of nucleated bubbles, while it is not justified in single particle quantum mechanics, as we explain. We mention possible applications of the real time formalism, including tunneling when the instanton vanishes, or when the imaginary time contour deformation is not possible, which may occur in cosmological settings.

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M. Hertzberg and M. Yamada
Fri, 19 Apr 19
20/50

Comments: 9 pages in double column format, 2 figures

Detect Gravitational Waves Using Twisted Light – Dipole Interaction of Photons and Gravitational Waves [CL]

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http://arxiv.org/abs/1904.05380


Motivated by the next generation of gravitational wave (GW) detectors, we study the wave mechanics of a twisted light beam in the GW perturbed spacetime. We found a new gravitational dipole interaction of photons and gravitational waves. Physically, this interaction is due to coupling between the angular momentum of twisted light and the GW polarizations. We demonstrate that for the higher-order Laguerre-Gauss (LG) modes, this coupling effect makes photons undergoing dipole transitions between different orbital-angular-momentum(OAM) eigenstates, and leads to some measurable optical features in the 2-D intensity pattern. It offers an alternative way to realize precision measurements of the gravitational waves, and enables us to extract more information about the physical properties of gravitational waves than the current interferometry. With a well-designed optical setup, this dipole interaction is expected to be justified in laboratories.

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L. Feng and Q. Wu
Fri, 12 Apr 19
23/62

Comments: 5 pages, 2 figures

Prospects for Searching Thermal Effects, Non-Newtonian Gravity and Axion-Like Particles: Cannex Test of the Quantum Vacuum [CL]

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http://arxiv.org/abs/1904.01642


We consider the CANNEX (Casimir And Non-Newtonian force EXperiment) test of the quantum vacuum intended for measuring the gradient of the Casimir pressure between two flat parallel plates at large separations and constraining parameters of the chameleon model of dark energy in cosmology. A modification of the measurement scheme is proposed that allows simultaneous measurements of both the Casimir pressure and its gradient in one experiment. It is shown that with several improvements the CANNEX test will be capable to strengthen the constraints on the parameters of the Yukawa-type interaction by up to an order of magnitude over a wide interaction range. The constraints on the coupling constants between nucleons and axion-like particles, which are considered as the most probable constituents of dark matter, could also be strengthened over a region of axion masses from 1 to 100 meV.

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G. Klimchitskaya, V. Mostepanenko, R. Sedmik, et. al.
Thu, 4 Apr 19
60/68

Comments: N/A

Cosmic Inflation, Quantum Information and the Pioneering Role of John S Bell in Cosmology [CL]

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http://arxiv.org/abs/1904.00083


According to the theory of cosmic inflation, the large scale structures observed in our Universe (galaxies, clusters of galaxies, Cosmic Background Microwave – CMB – anisotropy …) are of quantum mechanical origin. They are nothing but vacuum fluctuations, stretched to cosmological scales by the cosmic expansion and amplified by gravitational instability. At the end of inflation, these perturbations are placed in a two-mode squeezed state with the strongest squeezing ever produced in Nature (much larger than anything that can be made in the laboratory on Earth). This article studies whether astrophysical observations could unambiguously reveal this quantum origin by borrowing ideas from quantum information theory. It is argued that some of the tools needed to carry out this task have been discussed long ago by J. Bell in a, so far, largely unrecognized contribution. A detailed study of his paper and of the criticisms that have been put forward against his work is presented. Although J. Bell could not have realized it when he wrote his letter since the quantum state of cosmological perturbations was not yet fully characterized at that time, it is also shown that Cosmology and cosmic inflation represent the most interesting frameworks to apply the concepts he investigated. This confirms that cosmic inflation is not only a successful paradigm to understand the early Universe. It is also the only situation in Physics where one crucially needs General Relativity and Quantum Mechanics to derive the predictions of a theory and, where, at the same time, we have high-accuracy data to test these predictions, making inflation a playground of utmost importance to discuss foundational issues in Quantum Mechanics

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J. Martin
Tue, 2 Apr 19
66/90

Comments: 40 pages, 8 figures, to appear in “Universe”

Quantum non-linear evolution of inflationary tensor perturbations [CL]

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http://arxiv.org/abs/1903.12295


We study the quantum mechanical evolution of the tensor perturbations during inflation with non-linear tensor interactions. We first obtain the Lindblad terms generated by non-linear interactions by tracing out unobservable sub-horizon modes. Then we calculate explicitly the reduced density matrix for the super-horizon modes, and show that the probability of maintaining the unitarity of the squeezed state decreases in time. The decreased probability is transferred to other elements of the reduced density matrix including off-diagonal ones, so the evolution of the reduced density matrix describes the quantum-to-classical transition of the tensor perturbations. This is different from the classicality accomplished by the squeezed state, the suppression of the non-commutative effect, which is originated from the quadratic, linear interaction, and also maintains the unitarity. The quantum-to-classical transition occurs within 5 – 10 e-folds, faster than the curvature perturbation.

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J. Gong and M. Seo
Mon, 1 Apr 19
30/56

Comments: 39 pages

Machine learning and the physical sciences [CL]

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http://arxiv.org/abs/1903.10563


Machine learning encompasses a broad range of algorithms and modeling tools used for a vast array of data processing tasks, which has entered most scientific disciplines in recent years. We review in a selective way the recent research on the interface between machine learning and physical sciences.This includes conceptual developments in machine learning (ML) motivated by physical insights, applications of machine learning techniques to several domains in physics, and cross-fertilization between the two fields. After giving basic notion of machine learning methods and principles, we describe examples of how statistical physics is used to understand methods in ML. We then move to describe applications of ML methods in particle physics and cosmology, quantum many body physics, quantum computing, and chemical and material physics. We also highlight research and development into novel computing architectures aimed at accelerating ML. In each of the sections we describe recent successes as well as domain-specific methodology and challenges.

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G. Carleo, I. Cirac, K. Cranmer, et. al.
Wed, 27 Mar 19
11/74

Comments: N/A

Gravitational Direct Detection of Dark Matter [CL]

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http://arxiv.org/abs/1903.00492


The only coupling dark matter is guaranteed to have with the standard model is through gravity. Here we propose a concept for direct dark matter detection using only this gravitational coupling, enabling a new regime of detection. Leveraging dramatic advances in the ability to create, maintain, and probe quantum states of massive objects, we suggest that an array of quantum-limited impulse sensors may be capable of detecting the correlated gravitational force created by a passing dark matter particle. We present two concrete realizations of this scheme, using either mechanical resonators or freely-falling masses. With currently available technology, a meter-scale apparatus of this type could detect any dark matter candidate around the Planck mass or heavier.

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D. Carney, S. Ghosh, G. Krnjaic, et. al.
Tue, 5 Mar 19
15/73

Comments: 5 pages, 3 figures

Influence functionals, decoherence and conformally coupled scalars [CL]

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http://arxiv.org/abs/1902.09607


Some of the simplest modifications to general relativity involve the coupling of additional scalar fields to the scalar curvature. By making a Weyl rescaling of the metric, these theories can be mapped to Einstein gravity with the additional scalar fields instead being coupled universally to matter. The resulting couplings to matter give rise to scalar fifth forces, which can evade the stringent constraints from local tests of gravity by means of so-called screening mechanisms. In this talk, we derive evolution equations for the matrix elements of the reduced density operator of a toy matter sector by means of the Feynman-Vernon influence functional. In particular, we employ a novel approach akin to the LSZ reduction more familiar to scattering-matrix theory. The resulting equations allow the analysis, for instance, of decoherence induced in atom-interferometry experiments by these classes of modified theories of gravity.

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C. Burrage, C. Käding, P. Millington, et. al.
Fri, 1 Mar 19
42/59

Comments: 9 pages, JPCS format. Prepared for the proceedings of the 9th International Workshop DICE2018 Spacetime – Matter – Quantum Mechanics, 17-21 September 2018, Castiglioncello, Italy, to appear in the Journal of Physics: Conference Series. Presented by P. Millington

Quantum Distributions for the Plane Rotator [CL]

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http://arxiv.org/abs/1807.11816


Quantum phase-space distributions (Wigner functions) for the plane rotator are defined using wave functions expressed in both angle and angular momentum representations, with emphasis on the quantum superposition between the Fourier dual variable and the canonically conjugate coordinate. The standard quantization condition for angular momentum appears as necessary for consistency. It is shown that at finite temperature the time dependence of the quantum wave functions may provide classical sound waves. Non-thermal quantum entropy is associated with localization along the orbit.

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M. Grigorescu
Mon, 11 Feb 19
48/51

Comments: 9 pages, replaced to add Eq. (20)

Testing CSL with neutron stars [CL]

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http://arxiv.org/abs/1901.10963


A recent paper [arXiv:1901.05477] claims that the CSL model of spontaneous wave function collapse is ruled out by observations on heat flow from neutron stars. This type of system-a degenerate Fermi gas-is relevant as it represents the densest form of matter, potentially maximising CSL effects. As it turns out, this is not the case: to leading order, the CSL induced heating is the same as for ordinary matter, and neutron stars do not bound the CSL parameters significantly.

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S. Adler, A. Bassi, M. Carlesso, et. al.
Thu, 31 Jan 19
27/59

Comments: N/A

Symplectic Coarse-Grained Dynamics: Chalkboard Motion in Classical and Quantum Mechanics [CL]

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http://arxiv.org/abs/1901.06554


In the usual approaches to mechanics (classical or quantum) the primary object of interest is the Hamiltonian, from which one tries to deduce the solutions of the equations of motion (Hamilton or Schr\”odinger). In the present work we reverse this paradigm and view the motions themselves as being the primary objects. This is made possible by studying arbitrary phase space motions, not of points, but of (small) ellipsoids with the requirement that the symplectic capacity of these ellipsoids is preserved. This allows us to guide and control these motions as we like. In the classical case these ellipsoids correspond to a symplectic coarse graining of phase space, and in the quantum case they correspond to the “quantum blobs” we defined in previous work, and which can be viewed as minimum uncertainty phase space cells which are in a one-to-one correspondence with Gaussian pure states.

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M. Gosson
Wed, 23 Jan 19
100/111

Comments: N/A

Atomic source selection in space-borne gravitational wave detection [CL]

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http://arxiv.org/abs/1812.11348


Recent proposals for space-borne gravitational wave detectors based on atom interferometry rely on extremely narrow single-photon transition lines as featured by alkaline-earth metals or atomic species with similar electronic configuration. Despite their similarity, these species differ in key parameters such as abundance of isotopes, atomic flux, density and temperature regimes, achievable expansion rates, density limitations set by interactions, as well as technological and operational requirements. In this study, we compare viable candidates for gravitational wave detection with atom interferometry, contrast the most promising atomic species, identify the relevant technological milestones and investigate potential source concepts towards a future gravitational wave detector in space.

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S. Loriani, D. Schlippert, C. Schubert, et. al.
Tue, 1 Jan 19
4/55

Comments: N/A

Atomic source selection in space-borne gravitational wave detection [CL]

Posted on by

http://arxiv.org/abs/1812.11348


Recent proposals for space-borne gravitational wave detectors based on atom interferometry rely on extremely narrow single-photon transition lines as featured by alkaline-earth metals or atomic species with similar electronic configuration. Despite their similarity, these species differ in key parameters such as abundance of isotopes, atomic flux, density and temperature regimes, achievable expansion rates, density limitations set by interactions, as well as technological and operational requirements. In this study, we compare viable candidates for gravitational wave detection with atom interferometry, contrast the most promising atomic species, identify the relevant technological milestones and investigate potential source concepts towards a future gravitational wave detector in space.

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S. Loriani, D. Schlippert, C. Schubert, et. al.
Tue, 1 Jan 19
36/55

Comments: N/A

Chiral effects in magnetized quantum spinor matter in particle and astroparticle physics [CL]

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http://arxiv.org/abs/1812.11099


Quantum spinor matter in extremal conditions (high densities and temperatures, presence of strong magnetic fields) have drawn the attention of researchers in diverse areas of contemporary physics, ranging from cosmology, high-energy and astroparticle physics to condensed matter physics. We study an impact of the confining boundary conditions on the properties of physical systems with hot dense magnetized ultrarelativistic spinor matter and elucidate a significant role of boundaries for such systems.

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Y. Sitenko
Mon, 31 Dec 18
2/57

Comments: 14 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1612.08815, arXiv:1606.08241, arXiv:1603.09268

Open quantum dynamics induced by light scalar fields [CL]

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http://arxiv.org/abs/1812.08760


We consider the impact of a weakly-coupled environment comprising a light scalar field on the open dynamics of a quantum test mass. The light scalar is assumed to couple to matter either through a non-minimal coupling to gravity or, equivalently, through a Higgs portal. We introduce a novel approach for deriving the quantum master equation describing the evolution of the single-particle matrix element of the density operator from first-principles. Our approach draws on techniques of non-equilibrium quantum field theory, including the Feynman-Vernon influence functional and thermo-field dynamics, as well as a method of LSZ-like reduction. In addition, we show that non-Markovian effects, namely the violation of time-translational invariance due to finite-time effects, require us to introduce time-local counterterms in order to renormalize the resulting loop corrections consistently. This complementary and robust approach provides quantitative predictions and has the potential to shed new light on, for example, the divergences encountered in the context of gravitationally induced decoherence in general relativity. The resulting master equation features corrections to the coherent dynamics, as well as decoherence and momentum diffusion. We comment on the possibilities for experimental detection and the related challenges, and highlight possible pathways for further improvements.

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C. Burrage, C. Käding, P. Millington, et. al.
Mon, 24 Dec 18
42/47

Comments: 36 pages, 13 figures, revtex format, JHEP bibliography style; Comments are welcome

Open quantum dynamics induced by light scalar fields [CL]

Posted on by

http://arxiv.org/abs/1812.08760


We consider the impact of a weakly-coupled environment comprising a light scalar field on the open dynamics of a quantum test mass. The light scalar is assumed to couple to matter either through a non-minimal coupling to gravity or, equivalently, through a Higgs portal. We introduce a novel approach for deriving the quantum master equation describing the evolution of the single-particle matrix element of the density operator from first-principles. Our approach draws on techniques of non-equilibrium quantum field theory, including the Feynman-Vernon influence functional and thermo-field dynamics, as well as a method of LSZ-like reduction. In addition, we show that non-Markovian effects, namely the violation of time-translational invariance due to finite-time effects, require us to introduce time-local counterterms in order to renormalize the resulting loop corrections consistently. This complementary and robust approach provides quantitative predictions and has the potential to shed new light on, for example, the divergences encountered in the context of gravitationally induced decoherence in general relativity. The resulting master equation features corrections to the coherent dynamics, as well as decoherence and momentum diffusion. We comment on the possibilities for experimental detection and the related challenges, and highlight possible pathways for further improvements.

Read this paper on arXiv…

C. Burrage, C. Käding, P. Millington, et. al.
Mon, 24 Dec 18
31/47

Comments: 36 pages, 13 figures, revtex format, JHEP bibliography style; Comments are welcome

Open quantum dynamics induced by light scalar fields [CL]

Posted on by

http://arxiv.org/abs/1812.08760


We consider the impact of a weakly-coupled environment comprising a light scalar field on the open dynamics of a quantum test mass. The light scalar is assumed to couple to matter either through a non-minimal coupling to gravity or, equivalently, through a Higgs portal. We introduce a novel approach for deriving the quantum master equation describing the evolution of the single-particle matrix element of the density operator from first-principles. Our approach draws on techniques of non-equilibrium quantum field theory, including the Feynman-Vernon influence functional and thermo-field dynamics, as well as a method of LSZ-like reduction. In addition, we show that non-Markovian effects, namely the violation of time-translational invariance due to finite-time effects, require us to introduce time-local counterterms in order to renormalize the resulting loop corrections consistently. This complementary and robust approach provides quantitative predictions and has the potential to shed new light on, for example, the divergences encountered in the context of gravitationally induced decoherence in general relativity. The resulting master equation features corrections to the coherent dynamics, as well as decoherence and momentum diffusion. We comment on the possibilities for experimental detection and the related challenges, and highlight possible pathways for further improvements.

Read this paper on arXiv…

C. Burrage, C. Käding, P. Millington, et. al.
Mon, 24 Dec 18
40/47

Comments: 36 pages, 13 figures, revtex format, JHEP bibliography style; Comments are welcome

Universe's Primordial Quantum Memories [CL]

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http://arxiv.org/abs/1812.08749


We provide a very general argument showing that the Universe must have kept its quantum memories from an epoch much earlier than $60$ e-foldings before the end of inflation. The point is that a generic system of enhanced memory storage capacity exhibits a phenomenon of memory burden. Due to its universal nature this effect must be applicable to de Sitter since the latter has a maximal memory storage capacity thanks to its Gibbons-Hawking entropy. The primordial information pattern encoded in de Sitter memory initially costs very little energy. However, because of Gibbons-Hawking evaporation, the memory burden of the pattern grows in time and increasingly back reacts on the evaporation process. After a finite time the memory burden becomes unbearable and de Sitter quantum breaks. If inflation ended not long before its quantum break-time, the imprints of the primordial memory pattern can be observable. This provides a qualitatively new type of window in the Universe’s beginning, a sort of cosmic quantum hair.

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G. Dvali, L. Eisemann, M. Michel, et. al.
Fri, 21 Dec 18
66/72

Comments: 9 pages, 2 figures

Inflation with Spooky Correlations [CL]

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http://arxiv.org/abs/1811.03283


Models are developed to estimate properties of relic cosmic perturbations with “spooky” nonlocal correlations on the inflationary horizon, analogous to those previously posited for information on black hole event horizons. Scalar curvature perturbations are estimated to emerge with a dimensionless power spectral density $\Delta_S^2\approx H t_P$, the inflationary expansion rate $H$ in Planck units, larger than those from standard inflaton fluctuations, but consistent with current measurements of the power spectrum. It is shown that spooky nonlocality creates a unique, directionally antisymmetric signature that may be detectable in CMB anisotropy and large scale galaxy surveys.

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C. Hogan
Mon, 26 Nov 18
53/100

Comments: N/A

Bose-Einstein Condensates as Gravitational Wave Detectors [CL]

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http://arxiv.org/abs/1811.04468


We investigate a Bose-Einstein condensate (BEC) as a gravitational wave detector, and study its sensitivity by optimizing the properties of the condensate and the measurement duration. We show that detecting kilohertz gravitational waves is limited by current experimental techniques in squeezing BEC phonons, while at higher frequencies, decoherence due to phonon-phonon interaction gives the main limitation. Future improvements in technology to squeeze BEC states can make them competitive detectors for gravitational waves of astrophysical and/or cosmological origin.

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M. Robbins, N. Afshordi and R. Mann
Wed, 14 Nov 18
44/75

Comments: 18 pages, 3 figures

Quasar Correlation and Bell's Inequality [CEA]

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http://arxiv.org/abs/1811.00674


Viewing two sources at sufficient distance and angular separation can assure, by light-travel-time arguments, the acausality of their emitted photons. Using these photons to set different apparatus parameters in a laboratory-based quantum-mechanical experiment could ensure those settings are independent too, allowing a decisive, loophole-free test of Bell’s inequality. Quasars are a natural choice for such objects, as they are visible up to high redshift and pointlike. Yet applying them at the ultimate limit of the technique involves flux measurements in opposite directions on the sky. This presents a challenge to proving randomness against either noise or an underlying signal. By means of a “virtual” experiment and simple signal-to-noise calculations, bias in ground-based optical photometry while performing an Earth-wide test is explored, imposed by fluctuating sky conditions and instrumental errors including photometric zeropoints. Analysis for one useful dataset from the Gemini 8-meter telescopes is presented, using over 14 years of archival images obtained with their Multi-Object Spectrograph (GMOS) instrument pair, serendipitously sampling thousands of quasars up to 180 degrees apart. These do show correlation: an average pairwise broadband optical flux difference intriguingly consistent with the form of Bell’s inequality. That is interesting in itself, if not also a harm to experimental setting independence; some considerations for future observations are discussed.

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E. Steinbring
Mon, 5 Nov 18
18/49

Comments: 9 pages, 12 figures, submitted

Possible detection of nonclassical primordial gravitational waves with Hanbury Brown – Twiss interferometry [CL]

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http://arxiv.org/abs/1810.07604


We consider possible detection of nonclassicality of primordial gravitational waves (PGWs) by applying Hanbury Brown – Twiss (HBT) interferometry to cosmology. We characterize the nonclassicality of PGWs in terms of sub-Poissonian statistics that can be measured by the HBT interferometry. We show that the presence of classical sources during inflation makes us possible to detect nonclassical PGWs with the HBT interferometry. We present two examples that realize the classical sources during inflation. It turns out that PGWs with frequencies higher than 10 kHz enable us to detect their nonclassicality.

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S. Kanno and J. Soda
Thu, 18 Oct 18
27/75

Comments: 20 pages, 1 figure

Do particles and anti-particles really annihilate each other? [CL]

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http://arxiv.org/abs/1807.06428


Supported by results obtained with semi-classical quantization techniques, and with a quantum mechanical “square-root Klein-Gordon” operator, it is argued that Positronium (Ps) may exhibit a proper quantum-mechanical ground state whose energy level lies $\approx 2m c^2$ below its “hydrogenic (pseudo-) ground state” energy, where $m$ is the empirical rest mass of the electron. While the familiar hydrogenic pseudo-ground state of Ps is caused by the Coulomb attraction of electron and anti-electron, modified by small spin-spin and radiative QED corrections, the proper ground state is caused by the magnetic attraction between electron and anti-electron, which dominates over the electric one at short distances. This finding suggests that the familiar “annihilation” of electron and anti-electron is, in reality, simply yet another transition between two atomic energy levels, with the energy difference radiated off in form of photons — except that the energy difference is huge: about 1 MeV instead of the few eV in a hydrogenic transition. In their proper ground state configuration the two particles would be so close that they would electromagnetically neutralize each other for most practical purposes, thus giving the appearance of an annihilation. Once in such a tightly bound state such pairs would hardly interact with normal matter and not be noticeable — except through their gravitational effects in bulk! If the existence of such a low-energy ground state is confirmed it would imply that a significant part of the mysterious “dark matter” in the universe may consist of such matter-antimatter bound states.

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M. Kiessling
Thu, 11 Oct 18
25/72

Comments: Comments by peers on the previous version have been taken into account in this (minor) revision; two new references were added

Quantum Chameleons [CL]

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http://arxiv.org/abs/1809.10166


We initiate a quantum treatment of chameleon-like particles, deriving classical and quantum forces directly from the path integral. It is found that the quantum force can potentially dominate the classical one by many orders of magnitude. We calculate the quantum chameleon pressure between infinite plates, which is found to interpolate between the Casimir and the integrated Casimir-Polder pressures, respectively in the limits of full screening and no screening. To this end we calculate the chameleon propagator in the presence of an arbitrary number of one-dimensional layers of material. These results are applied to the symmetron dark energy model which turns out to be strongly constrained by quantum forces probed by molecular spectroscopy and the E\”otwash experiment. For the E\”otwash experiment we exactly take into account the effects of the intermediate shielding sheet by computing the symmetron propagator in five layers and find that the presence of the sheet enhances the quantum force by two orders of magnitude. As a result the E\”otwash experiment becomes sensitive to the quantum Casimir pressure from chameleon-like particles, constraining a large part of the symmetron parameter space.

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P. Brax and S. Fichet
Tue, 9 Oct 18
52/77

Comments: 5 pages, 3 figures

Scattering of light dark matter in atomic clocks [CL]

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http://arxiv.org/abs/1810.01632


We present a detailed analysis of the effect of light Dark Matter (DM) on atomic clocks, for the case where DM mass and density are such that occupation numbers are low and DM must be considered as particles scattering off the atoms, rather than a classical field. We show that the resulting atomic clock frequency shifts are first order in the scattering amplitudes, and particularly suited to constrain DM models in the regime where the DM mass $m_\chi \ll$ GeV. We provide some rough order of magnitude estimates of sensitivity that can be confronted to any DM model that allows for non zero differential scattering amplitudes of the two atomic states involved in the clock.

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P. Wolf, R. Alonso and D. Blas
Thu, 4 Oct 18
4/72

Comments: 10 pages, 1 figure, 1 table

Exploring the ultra-light to sub-MeV dark matter window with atomic clocks and co-magnetometers [CL]

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http://arxiv.org/abs/1810.00889


Particle dark matter could have a mass anywhere from that of ultralight candidates, $m_\chi\sim 10^{-21}\,$eV, to scales well above the GeV. Conventional laboratory searches are sensitive to a range of masses close to the weak scale, while new techniques are required to explore candidates outside this realm. In particular lighter candidates are difficult to detect due to their small momentum. Here we study two experimental set-ups which {\it do not require transfer of momentum} to detect dark matter: atomic clocks and co-magnetometers. These experiments probe dark matter that couples to the spin of matter via the very precise measurement of the energy difference between atomic states of different angular momenta. This coupling is possible (even natural) in most dark matter models, and we translate the current experimental sensitivity into implications for different dark matter models. It is found that the constraints from current atomic clocks and co-magnetometers can be competitive in the mass range $m_\chi\sim 10^{-21}-10^3\,$eV, depending on the model. We also comment on the (negligible) effect of different astrophysical neutrino backgrounds.

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R. Alonso, D. Blas and P. Wolf
Wed, 3 Oct 18
25/64

Comments: 50 pages, 9 figures, 5 tables

Quantum measurement and fuzzy dark matter [CL]

Posted on by

http://arxiv.org/abs/1809.04946


It has been suggested that dark matter is a superfluid of particles whose masses are on the rough order of $10^{-22}$ eV. Since the occupation numbers are huge, the state is coherent, and the speeds typical of orbital velocities in halos, it has generally been assumed that a classical effective non-relativistic treatment is adequate. However, the Compton wavelength would be $\sim 1\, {\rm pc}$, and around the Compton scale concerns about some aspects of quantum measurement theory, known in principle but not quantitatively significant in previous cases, become pronounced. I estimate here the stress–energy operator, averaged over a few Compton wavelengths; a rough but useful approximation has a remarkably simple form. Conventional quantum measurement theory gives physically unacceptable results: a thought-experiment to measure the stress–energy is described which would involve only a modest apparatus but would excite particles in the observation volume to relativistic energies; these particles would escape the Galaxy, and there would be a substantial violation of energy conservation. Related foundational questions come up: the meaning of measurements of observables with continuous spectra, and the problem of predicting when measurements occur. The effective classical theory of fuzzy dark matter is not affected; however, the underlying quantum theory cannot be regarded as satisfactory without resolving these issues. But we may interpret the results more broadly. The macroscopic Compton scale amplifies inadequacies of measurement theory which have not previously seemed pressing.

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A. Helfer
Fri, 14 Sep 18
43/65

Comments: 12 pages, accepted by PRD

Quantum-Assisted Telescope Arrays [CL]

Posted on by

http://arxiv.org/abs/1809.03396


Quantum networks provide a platform for astronomical interferometers capable of imaging faint stellar objects. In a recent work [arXiv:1809.01659], we presented a protocol that circumvents transmission losses with efficient use of quantum resources and modest quantum memories. Here, we analyze a number of extensions to that scheme. We show that it can be operated as a truly broadband interferometer and generalized to multiple sites in the array. We also analyze how imaging based on the quantum Fourier transform provides improved signal-to-noise ratio compared to classical processing. Finally, we discuss physical realizations including photon detection-based quantum state transfer.

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E. Khabiboulline, J. Borregaard, K. Greve, et. al.
Tue, 11 Sep 18
12/62

Comments: 9 pages, 8 figures

Spectrum of cosmological correlation from vacuum fluctuation of Stringy Axion in entangled de Sitter space [CL]

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http://arxiv.org/abs/1809.02905


In this work, we study the impact of quantum entanglement on the two-point correlation function and the associated primordial power spectrum of mean square vacuum fluctuation in a bipartite quantum field theoretic system. The field theory that we consider is the effective theory of axion field arising from Type IIB string theory compactified to four dimensions. We compute the expression for the power spectrum of vacuum fluctuation in three different approaches, namely (1) field operator expansion (FOE) technique with the quantum entangled state, (2) reduced density matrix (RDM) formalism with mixed quantum state and (3) the method of non-entangled state (NES). For massless axion field, in all these three formalism, we reproduce, at the leading order, the exact scale-invariant power spectrum which is well known in the literature. We observe that due to quantum entanglement, the sub-leading terms for these thee formalisms are different. Thus, such correction terms break the degeneracy among the analysis of the FOE, RDM and NES formalisms in the super-horizon limit. On the other hand, for massive axion field, we get a slight deviation from scale invariance and exactly quantify the spectral tilt of the power spectrum in small scales. Apart from that, for massless and massive axion field, we find distinguishable features of the power spectrum for the FOE, RDM, and NES on the large scales, which is the result of quantum entanglement. We also find that such large-scale effects are comparable to or greater than the curvature radius of the de Sitter space. Most importantly, in the near future, if experiments probe for early universe phenomena, one can detect such small quantum effects. In such a scenario, it is possible to test the implications of quantum entanglement in primordial cosmology.

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S. Choudhury and S. Panda
Tue, 11 Sep 18
42/62

Comments: 71 pages, 13 figures, 1 table

Nonlocal Optical Interferometry with Quantum Networks [CL]

Posted on by

http://arxiv.org/abs/1809.01659


We propose a method for optical interferometry in telescope arrays assisted by quantum networks. In our approach, the quantum state of incoming photons along with an arrival time index is stored in a binary qubit code at each receiver. Nonlocal retrieval of the quantum state via entanglement-assisted parity checks at the expected photon arrival rate allows for direct extraction of phase difference, effectively circumventing transmission losses between nodes. Compared to prior proposals, our scheme, based on efficient quantum data compression, offers an exponential decrease in required entanglement bandwidth. Experimental implementation is then feasible with near-term technology, enabling optical imaging of astronomical objects akin to well-established radio interferometers and pushing resolution beyond what is practically achievable classically.

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E. Khabiboulline, J. Borregaard, K. Greve, et. al.
Fri, 7 Sep 18
9/65

Comments: 6 + 6 pages, 3 + 1 figures

Condensate Dynamics with Non-Local Interactions [CEA]

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http://arxiv.org/abs/1808.06378


Systems of identical particles possessing non-local interactions are capable of exhibiting extra-classical properties beyond the characteristic quantum length scales. This letter derives the dynamics of such systems in the non-relativistic and degenerate limit, showing the effect of exchange symmetry and correlations on structure both in and out of equilibrium. Such descriptions may be crucial to understanding systems ranging from nuclei to dark matter. Appropriate limits for restoring the mean-field description are also discussed.

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E. Lentz, T. Quinn and L. Rosenberg
Tue, 21 Aug 18
66/71

Comments: 4 pages, 1 figure, submitted to PRD Rapid Communications

Doubly Special Relativity and Photons at the Planck Scale [CL]

Posted on by

http://arxiv.org/abs/1808.01243


In this paper, within the approach to doubly special relativity (DSR) suggested by Magueijo and Smolin, a new algebraically justified rule of so-called $\kappa$-addition for the energies of particles is proposed. This rule makes it possible to introduce the nonlinear $\kappa$-dependent Hamiltonian for one-mode multi-photon (sub)system. On its base, with different modes treated as independent, the thermodynamics of black-body radiation is explored within DSR, and main thermodynamic quantities are obtained. In their derivation, we use both the analytical tools within mean field approximation (MFA) and numerical evaluations based on exact formulas. The entropy of one-mode subsystem turns out to be finite (bounded). Another unusual result is the existence of threshold temperature above which radiation is present. Specific features of the obtained results are explained and illustrated with a number of plots. Comparison with some works of relevance is given.

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W. Chung, A. Gavrilik and A. Nazarenko
Fri, 17 Aug 18
50/53

Comments: v2: 16 pages, 6 figures, PACS numbers corrected, small textual changes, two references added, appendix dropped, adapted for submission

Matter parametric neutrino flavor transformation through Rabi resonances [CL]

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http://arxiv.org/abs/1807.10219


We consider the flavor transformation of neutrinos through oscillatory matter profiles. We show that the neutrino oscillation Hamiltonian in this case describes a Rabi system with an infinite number of Rabi modes. We further show that, in a given physics problem, the majority of the Rabi modes have too small amplitudes to be relevant. We also go beyond the rotating wave approximation and derive the relative detuning of the Rabi resonance when multiple Rabi modes with small amplitudes are present. We provide an explicit criterion of whether an off-resonance Rabi mode can affect the parametric flavor transformation of the neutrino.

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L. Ma, S. Shalgar and H. Duan
Fri, 27 Jul 18
4/75

Comments: 7 pages, 3 figures

Testing spontaneous collapse through bulk heating experiments: estimate of the background noise [CL]

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http://arxiv.org/abs/1807.03067


Models of spontaneous wave function collapse predict a small heating rate for a bulk solid, as a result of coupling to the noise field that causes collapse. This rate is small enough that ambient radioactivity and cosmic ray flux on the surface of the earth can mask the heating due to spontaneous collapse. In this paper we estimate the background noise due to gamma-radiation and cosmic ray muon flux, at different depths. We demonstrate that a low-temperature underground experiment at a depth of about 6.5 km.w.e. can detect the bulk heating for a collapse rate $\lambda$ of $10^{-16}$ s$^{-1}$ using presently available technology.

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R. Mishra, A. Vinante and T. Singh
Tue, 10 Jul 18
2/79

Comments: 10 pages, 4 figures, 2 tables

Entangled-path interferometer simpler, faster than LISA [CL]

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http://arxiv.org/abs/1807.02159


Entangled light can provide a seminal improvement in resolution sensitivity even without achieving Heisenberg limit in a single channel. In this paper, based on the back-of-the-envelope type calculations, I demonstrate an alternative path to space based long-arm interferometer. Its advantage with respect to LISA is that it does not require complex satellites with many active components to achieve similar resolution.

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P. Lerner
Mon, 9 Jul 18
22/43

Comments: N/A

Quantum noise cancellation in asymmetric speed meters with balanced homodyne readout [CL]

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http://arxiv.org/abs/1806.05488


Sagnac speed meter (SSM) topology is known as an alternative technique to reduce quantum back-action in gravitational-wave interferometers. However, any potential imbalance of the main beamsplitter was shown to reduce the quantum noise superiority of speed meter at low frequencies, caused due to increased laser noise coupling to the detection port. In this paper, we show that implementing balanced homodyne readout scheme and for a particular choice of the local oscillator (LO) delivery port, the excess laser noise contribution to quantum noise limited sensitivity (QNLS) is partly compensated and the speed meter sensitivity can outperform state-of-the-art position meters. This can be achieved by picking the local oscillator from interferometer reflection (\textit{co-moving} LO) or the main beamsplitter anti-reflective coating surface (BSAR LO). We also show that this relaxes the relative intensity noise (RIN) requirement of the input laser. For example, for a beam splitter imbalance of $0.1 \%$ in Glasgow speed meter proof of concept experiment, the RIN requirement at frequency of 100Hz decreases from $4\times 10^{-10}/\sqrt{\rm Hz}$ to $4\times 10^{-7}/\sqrt{\rm Hz}$, moving the RIN requirement from a not practical achievable value to one which is routinely achieved with moderate effort.

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T. Zhang, E. Knyazev, S. Steinlechner, et. al.
Fri, 15 Jun 18
2/54

Comments: N/A

The `unitarity problem' of Higgs inflation in the light of collapse dynamics [CEA]

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http://arxiv.org/abs/1805.11527


Higgs inflation scenario is one of the most compelling models of inflation at present time. It not only explains the observed data well, but also provides means to include the inflaton field within the well understood Standard Model of particle physics, without invoking any need for its extension. Despite this, due to the requirement of large non-minimal coupling to the curvature scalar of the inflaton field, or in this case the Higgs field, this model suffers from a problem often called as the unitarity' or thenaturalness’ problem. On the other hand, to address the longstanding interpretational issue' of quantum to classical transition of the primordial modes, the collapse dynamics of quantum mechanics has recently been included into the inflationary mechanism. We show that inclusion of such collapse mechanism in Higgs inflation helps alleviate theunitarity problem’ to a great deal.

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S. Das
Wed, 30 May 18
16/65

Comments: 14 pgs, no figure

On the quantitative calculation of the cosmological constant of the quantum vacuum [CL]

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http://arxiv.org/abs/1805.10440


It is widely believed that as one of the candidates for dark energy, the cosmological constant should relate directly with the quantum vacuum. Despite decades of theoretical effects, however, there is still no quantitative interpretation of the observed cosmological constant. In this work, we consider the quantum state of the whole universe including the quantum vacuum. Everett’s relative-state formulation, vacuum quantum fluctuations and the validity of Einstein’s field equation at macroscopic scales imply that our universe wave function might be a superposition of states with different cosmological constants. In the density matrix formulation of this quantum universe, the quasi-thermal equilibrium state is described by a specific cosmological constant with the maximum probability. Without any fitting parameter, the ratio between the vacuum energy density due to the cosmological constant (dark energy) and the critical density of the universe is 68.85% based on simple equations in our theoretic model, which agrees very well with the best current astronomical observations of 68.5%.

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H. Xiong
Tue, 29 May 18
70/73

Comments: 16 pages, 1 figure

Unravelling Cosmological Perturbations [CL]

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http://arxiv.org/abs/1804.07637


We explain in detail the quantum-to-classical transition for the cosmological perturbations using only the standard rules of quantum mechanics: the Schrodinger equation and Born’s rule applied to a subsystem. We show that the conditioned, i.e. intrinsic, pure state of the perturbations, is driven by the interactions with a generic environment, to become increasingly localized in field space as a mode exists the horizon during inflation. With a favourable coupling to the environment, the conditioned state of the perturbations becomes highly localized in field space due to the expansion of spacetime by a factor of roughly exp(-c N), where N~50 and c is a model dependent number of order 1. Effectively the state rapidly becomes specified completely by a point in phase space and an effective, classical, stochastic process emerges described by a classical Langevin equation. The statistics of the stochastic process is described by the solution of the master equation that describes the perturbations coupled to the environment.

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T. Hollowood
Mon, 23 Apr 18
43/63

Comments: 21 pages

Photon-graviton scattering: a new way to detect anisotropic gravitational waves? [CL]

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http://arxiv.org/abs/1804.06298


Gravitons are the quantum counterparts of gravitational waves in low-energy theories of gravity. Using Feynman rules one can compute scattering amplitudes describing the interaction between gravitons and other fields. Here, we consider the interaction between gravitons and photons. Using the quantum Boltzmann equation formalism, we derive fully general equations describing the radiation transfer of photon polarization, due to the forward scattering with gravitons. We show that the Q and U photon linear polarization modes couple with the V photon circular polarization mode, if gravitons have anisotropies in their power-spectrum statistics. As an example, we apply our results to the case of primordial gravitons, considering models of inflation where an anisotropic primordial graviton distribution is produced. Finally, we evaluate the effect on Cosmic Microwave Background (CMB) polarization, showing that in general the expected effects on the observable CMB frequencies are very small. However, our result is promising, since it could provide a novel tool for detecting anisotropic backgrounds of gravitational waves, as well as for getting further insight on the physics of gravitational waves.

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N. Bartolo, A. Hoseinpour, G. Orlando, et. al.
Wed, 18 Apr 18
20/74

Comments: 15 pages, 1 figure

Gravity induced geometric phases and entanglement in spinors and neutrinos: Gravitational Zeeman effect [CL]

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http://arxiv.org/abs/1802.10377


We show Zeeman-like splitting in the energy of spinors propagating in the background gravitational field, analogous to the spinors in electromagnetic field, otherwise termed as Gravitational Zeeman Effect. These spinors are also found to acquire a geometric phase, in a similar way as they do in the presence of magnetic fields. Based on this result, we investigate geometric phases acquired by neutrinos propagating in a strong gravitational field. We also explore entanglement of neutrino states due to gravity which could induce neutrino-antineutrino oscillation in the first place. We show that entangled states also acquire geometric phases which are determined by the relative strength between gravitational field and neutrino masses.

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B. Mukhopadhyay and S. Ganguly
Thu, 1 Mar 18
33/66

Comments: 23 pages including 5 figures; Comments are welcome

Observational constraints on quantum decoherence during inflation [CEA]

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http://arxiv.org/abs/1801.09949


Since inflationary perturbations must generically couple to all degrees of freedom present in the early Universe, it is more realistic to view these fluctuations as an open quantum system interacting with an environment. Then, on very general grounds, their evolution can be modelled with a Lindblad equation. This modified evolution leads to quantum decoherence of the system, as well as to corrections to observables such as the power spectrum of curvature fluctuations. On one hand, current cosmological observations constrain the properties of possible environments and place upper bounds on the interaction strengths. On the other hand, imposing that decoherence completes by the end of inflation implies lower bounds on the interaction strengths. Therefore, the question arises of whether successful decoherence can occur without altering the power spectrum. In this paper, we systematically identify all scenarios in which this is possible. As an illustration, we discuss the case in which the environment consists of a heavy test scalar field. We show that this realises the very peculiar configuration where the correction to the power spectrum is quasi scale invariant. In that case, the presence of the environment improves the fit to the data for some inflationary models but deteriorates it for others. This clearly demonstrates that decoherence is not only of theoretical importance but can also be crucial for astrophysical observations.

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J. Martin and V. Vennin
Wed, 31 Jan 18
45/65

Comments: 53 pages without appendices (total 86 pages), 11 figures

Interstellar Communication. VIII. Hard limits on the number of bits per photon [IMA]

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http://arxiv.org/abs/1801.06218


A photon can encode several bits of information based on an alphabet of its time of arrival, energy, and polarization. Heisenberg’s uncertainty principle places a limit on measuring pairs of physical properties of a particle, limiting the maximal information efficiency to <59 bits per photon in practice, and <171 bits per photon at Planck energy, at a data rate of one photon per second.

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M. Hippke
Mon, 22 Jan 2018
39/52

Comments: 3 pages, 1 figure

Entangled de Sitter from Stringy Axionic Bell pair II: An analysis using $α$ vacua [CL]

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http://arxiv.org/abs/1712.08299


In this work, we study the phenomena of quantum entanglement by computing de Sitter entanglement entropy from Von Newmann measure. For this purpose we consider a bipartite quantum field theoretic setup in presence of axion originating from ${\bf Type~ II~B}$ string theory. We consider the initial vaccum to be CPT invariant non adiabatic $\alpha$ vacua state under ${\bf SO(1,4)}$ ismometry, which is characterized by a real one parameter family. To implement this technique we use a ${\bf S^2}$ which divide the de Sitter into two exterior and interior sub regions. First we derive the wave function of axion in an open chart for $\alpha$ vacua by applying Bogoliubov transformation on the solution for Bunch Davies vacuum state. Further we quantify the density matrix by tracing over the contribution from exterior region. Using this result we derive entanglement entropy, R$\acute{e}$nyi entropy and explain the long range quantum effects in primordial cosmological correlations. We also provide a comparison between the results obtained from Bunch Davies vacuum and the generalized $\alpha$ vacua, which implies that the amount of quantum entanglement and the long range effects are larger for non zero value of the parameter $\alpha$. Most significantly, our derived results for $\alpha$ vacua provides the necessary condition for generating non zero entanglement entropy in primordial cosmology.

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S. Choudhury and S. Panda
Mon, 25 Dec 17
14/37

Comments: 68 pages, 26 figures, 9 tables

Interstellar communication. V. Introduction to photon information efficiency (in bits per photon) [IMA]

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http://arxiv.org/abs/1712.05682


How many bits of information can a single photon carry? Intuition says “one”, but this is incorrect. With an alphabet based on the photon’s time of arrival, energy, and polarization, several bits can be encoded. In this introduction to photon information efficiency, we explain how to calculate the maximum number of bits per photon depending on the number of encoding modes, noise, and losses.

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M. Hippke
Mon, 18 Dec 17
29/49

Comments: 3 pages, 1 figure. Useful introduction for the previous parts of this series: arXiv:1706.03795, arXiv:1706.05570, arXiv:1711.05761, arXiv:1711.07962