Tag Archives: Superconductivity

Exploring $^3P_0$ Superfluid in Dilute Spin-Polarized Neutron Matter [CL]

Posted on by

http://arxiv.org/abs/2305.08690


We study the theoretical possibility of $^3P_0$ neutron superfluid in dilute spin-polarized neutron matter, which may be relevant to the crust region of a magnetized neutron star. In such a dilute regime where the neutron Fermi energy is less than 1 MeV, the $^1S_0$ neutron superfluid can be exhausted by a strong magnetic field of the compact star. At low-energy limit relevant for dilute neutron matter, the $^3P_0$ interaction is stronger than the $^3P_2$ one, which is believed to induce the triplet superfluid in the core. We present the ground-state phase diagram of dilute neutron matter with respect to the magnetic field and numerically estimate the critical temperature of $^3P_0$ neutron superfluid, which exceeds $10^7$~K.

Read this paper on arXiv…

H. Tajima, H. Funaki, Y. Sekino, et. al.
Tue, 16 May 23
61/83

Comments: 6 pages, 3 figures

Stability of interlinked neutron vortex and proton flux-tube arrays in a neutron star — III. Proton feedback [HEAP]

Posted on by

http://arxiv.org/abs/2305.04482


The coupled, time-dependent Gross-Pitaevskii and Ginzburg-Landau equations are solved simultaneously in three dimensions to investigate the equilibrium state and far-from-equilibrium, spin-down dynamics of an interpenetrating neutron superfluid and proton type-II superconductor, as an idealized description of the outer core of a neutron star. The simulations generalize previous calculations without the time-dependent Ginzburg-Landau equation, where proton feedback is absent. If the angle $\theta$ between the rotation and magnetic axes does not equal zero, the equilibrium state consists of geometrically complicated neutron vortex and proton flux-tube tangles, as the topological defects pin to one another locally but align with different axes globally. During spin-down, new types of motion are observed. For $\theta = 0$, entire vortices pair rectilinearly with flux tubes and move together while pinned. For $\theta \neq 0$, vortex segments pair with segments from one or more flux tubes, and the paired segments move together while pinned. The degree to which proton feedback impedes the deceleration of the crust is evaluated as a function of $\theta$ and the pinning strength, $\eta$. Key geometric properties of vortex-flux-tube tangles, such as filament length, mean curvature, and polarity are analysed. It is found that proton feedback smooths the deceleration of the crust, reduces the rotational glitch sizes, and stabilizes the vortex tangle dynamics. The dimensionless control parameters in the simulations are mutually ordered to match what is expected in a real neutron star, but their central values and dynamics ranges differ from reality by many orders of magnitude due to computational limitations.

Read this paper on arXiv…

K. Thong, A. Melatos and L. Drummond
Tue, 9 May 23
60/88

Comments: N/A

CAPP Axion Search Experiments with Quantum Noise Limited Amplifiers [CL]

Posted on by

http://arxiv.org/abs/2304.07222


The axion is expected to solve the strong CP problem of quantum chromodynamics and is one of the leading candidates for dark matter. CAPP in South Korea has several axion search experiments based on cavity haloscopes in the frequency range of 1-6 GHz. The main effort focuses on operation of the experiments with the highest possible sensitivity. It requires maintenance of the haloscopes at the lowest physical temperature in the range of mK and usage of low noise components to amplify the weak axion signal. We report development and operation of low noise amplifiers for 5 haloscope experiments targeting at different frequency ranges. The amplifiers show noise temperatures approaching the quantum limit.

Read this paper on arXiv…

S. Uchaikin, B. Ivanov, J. Kim, et. al.
Mon, 17 Apr 23
40/51

Comments: 6 pages, 7 figures, 29th International Conference on Low Temperature Physics, August 18-24, 2022, Sapporo, Japan

Polaronic Proton and Diproton Clustering in Neutron-Rich Matter [CL]

Posted on by

http://arxiv.org/abs/2304.00535


We show that strong spin-triplet neutron-proton interaction causes polaronic protons to occur in neutron matter at subnuclear densities and nonzero temperature. As the neutron density increases, proton spectra exhibit a smooth crossover from a bare impurity to a repulsive polaron branch; this branch coexists with an attractive polaron branch. With the neutron density increased further, the attractive polarons become stable with respect to deuteron formation. For two adjacent protons, we find that the polaron effects and the neutron-mediated attraction are sufficient to induce a bound diproton, which leads possibly to diproton formation in the surface region of neutron-rich nuclei in laboratories as well as in neutron stars.

Read this paper on arXiv…

H. Tajima, H. Moriya, W. Horiuchi, et. al.
Tue, 4 Apr 23
20/111

Comments: 6 pages, 4 figures (8 pages, 6 figures in the supplement)

Voltage Fluctuations in ac Biased Superconducting Transition-Edge Sensors [CL]

Posted on by

http://arxiv.org/abs/2210.06869


We present a detailed analysis of the fundamental noise sources in superconducting transition-edge sensors (TESs), ac voltage biased at MHz frequencies and treated as superconducting weak links. We have studied the noise in the resistive transition as a function of bath temperature of several detectors with different normal resistances and geometries. We show that the excess noise, typically observed in the TES electrical bandwidth, can be explained by the equilibrium Johnson noise of the quasiparticles generated within the weak link. The fluctuations at the Josephson frequency and higher harmonics contribute significantly to the measured voltage noise at the detector bandwidth through the nonlinear response of the weak link with a sinusoidal current-phase relation.

Read this paper on arXiv…

L. Gottardi, M. Wit, E. Taralli, et. al.
Fri, 14 Oct 22
15/75

Comments: 9 pages, 7 figures

A Review of X-ray Microcalorimeters Based on Superconducting Transition Edge Sensors for Astrophysics and Particle Physics [IMA]

Posted on by

http://arxiv.org/abs/2210.06914


The state-of-the-art technology of X-ray microcalorimeters based on superconducting transition edge sensors (TESs), for applications in astrophysics and particle physics, is reviewed. We will show the advance in understanding the detector physics and describe the recent breakthroughs in the TES design that are opening the way towards the fabrication and the read-out of very large arrays of pixels with unprecedented energy resolution. The most challenging low temperature instruments for space- and ground-base experiments will be described.

Read this paper on arXiv…

L. Gottardi and K. Nagayoshi
Fri, 14 Oct 22
50/75

Comments: 48 pages, 14 figures, published in Appl. Sci. 2021, 11, 3793

Transition-Edge Sensors for cryogenic X-ray imaging spectrometers [IMA]

Posted on by

http://arxiv.org/abs/2210.06617


Large arrays of superconducting transition-edge sensor (TES) microcalorimeters are becoming the key technology for future space-based X-ray observatories and ground-based experiments in the fields of astrophysics, laboratory astrophysics, plasma physics, particle physics and material analysis. Thanks to their sharp superconducting-to-normal transition, TESs can achieve very high sensitivity in detecting small temperature changes at very low temperature. TES based X-ray detectors are non-dispersive spectrometers bringing together high resolving power, imaging capability and high-quantum efficiency simultaneously. In this chapter, we highlight the basic principles behind the operation and design of TESs, and their fundamental noise limits. We will further elaborate on the key fundamental physics processes that guide the design and optimization of the detector. We will then describe pulse-processing and important calibration considerations for space flight instruments, before introducing novel multi-pixel TES designs and discussing applications in future X-ray space missions over the coming decades.

Read this paper on arXiv…

L. Gottardi and S. Smith
Fri, 14 Oct 22
71/75

Comments: 45 pages, 18 figures. This Chapter will appear in the Section “Detectors for X-ray Astrophysics” (Section Editors: J-W. den Harder, M. Feroci, N. Meidinger) of the “Handbook of X-ray and Gamma-ray Astrophysics” (Editors in chief: C. Bambi and A. Santangelo)

Signatures and Detection Prospects for sub-GeV Dark Matter with Superfluid Helium [CL]

Posted on by

http://arxiv.org/abs/2208.14474


We explore the possibility of using superfluid helium for direct detection of sub-GeV dark matter (DM). We discuss the relevant phenomenology resulting from the scattering of an incident dark matter particle on a Helium nucleus. Rather than directly exciting quasi-particles, DM in this mass range will interact with a single He atom, triggering an atomic cascade which eventually also includes emission and thermalization of quasi-particles. We present in detail the analytical framework needed for modeling these processes and determining the resulting flux of quasi-particles. We propose a novel method for detecting this flux with modern force-sensitive devices, such as nanoelectro-mechanical system (NEMS) oscillators, and derive the sensitivity projections for a generic sub-GeV DM detection experiment using such sensors.

Read this paper on arXiv…

Y. You, J. Smolinsky, W. Xue, et. al.
Thu, 1 Sep 22
33/68

Comments: 28 pages, 12 figures

Oscillating Magnetized Color Superconducting Quark Stars [HEAP]

Posted on by

http://arxiv.org/abs/2205.07928


The main objective of this work is to study the structure, composition, and oscillation modes of color superconducting quark stars with intense magnetic fields. We adopted the MIT bag model within the color superconductivity CFL framework, and we included the effects of strong magnetic fields to construct the equation of state of stable quark matter. We calculated observable quantities, such as the mass, radius, frequency, and damping time of the oscillation fundamental $f$ mode of quark stars, taking into account current astrophysical constraints. The results obtained show that color superconducting magnetized quark stars satisfy the constraints imposed by the observations of massive pulsars and gravitational wave events. Furthermore, the quantities associated with the oscillation $f$ mode of these objects fit the universal relationships for compact objects. In the context of the new multi-messenger gravitational wave astronomy era and the future asteroseismology of neutron stars, we hope that our results contribute to the understanding of the behavior of dense matter and compact objects.

Read this paper on arXiv…

M. Celi, M. Mariani, M. Orsaria, et. al.
Wed, 18 May 22
11/66

Comments: N/A

A Proposal for Detecting Superconductivity in Neutron Stars [CL]

Posted on by

http://arxiv.org/abs/2205.08259


It has been theoretically studied that superconductivity (SC) can reflect gravitational wave (GW) in the weak gravitational field limit [1]. Based on the feature, in this article an experimental proposal is raised to probe the expected SC in neutron star by means of GW detection. Two binary systems are considered, neutron star-black hole and binary neutron star systems, with weak gravitational field condition imposed. Non-negligible modulation on the total signal caused by the GW reflection is found, which contributes frequency components different from GW frequency. Correspondingly, in time domain, the modulation leads to fluctuation on the amplitude and phase, increasing with the angular velocity. We show that such modulation signals are detectable by the Cosmic Explorer at $100\,\mbox{Mpc}$. Identification of those signals can evince the existence of the long-sought SC in neutron stars as well as the exotic superconductivity-induced GW reflection.

Read this paper on arXiv…

Y. Gao, J. Yang, Z. Zhu, et. al.
Wed, 18 May 22
57/66

Comments: 5 pages, 7 figures

Density filamentation nonlinearly driven by the Weibel instability in relativistic beam plasmas [CL]

Posted on by

http://arxiv.org/abs/2205.03795


Density filamentation has been observed in many beam-plasma simulations and experiments. Because current filamentation is a pure transverse mode, charge density filamentation cannot be produced directly by the current filamentation process. To explain this phenomenon, several mechanisms are proposed such as the coupling of the Weibel instability to the two-stream instability, coupling to the Langmuir wave, differences in thermal velocities between the beam and return currents, the magnetic pressure gradient force, etc. In this paper, it is shown that the gradient of the Lorentz factor can, in fact, represent the nonlinear behavior of a plasma fluid and further that the nonuniform Lorentz factor distribution can give rise to electrostatic fields and density filaments. Simulation results together with theoretical analyses are presented.

Read this paper on arXiv…

C. Huynh, C. Ryu and C. Kim
Tue, 10 May 22
70/70

Comments: N/A

Multiplexable frequency retuning of MKID arrays using their non-linear kinetic inductance [IMA]

Posted on by

http://arxiv.org/abs/2204.05715


Microwave Kinetic Inductance Detector (MKID) arrays are currently being developed and deployed for astronomical applications in the visible and near infrared and for sub-millimetre astronomy. One of the main drawbacks of MKIDs is that large arrays would exhibit a pixel yield, the percentage of individually distinguishable pixels to the total number of pixels, of 75 – 80 %. Imperfections arising during the fabrication can induce an uncontrolled shift in the resonance frequency of individual resonators which can end up resonating at the same frequency of a different resonator. This makes a number of resonators indistinguishable and therefore unusable for imaging. This paper proposes an approach to individually re-tune the colliding resonators in order to remove the degeneracy and increase the number of MKIDs with unique resonant frequencies. The frequency re-tuning is achieved through a DC bias of the resonator, the kinetic inductance of a superconducting thin film is current dependent and its dependence is non linear. Even though this approach has been already proposed, an innovative pixel design, described in this paper, may solve two issues previously described in literature such as increased electromagnetic losses to the DC-bias line, and the multiplexibility of multiple resonators on a single feedline.

Read this paper on arXiv…

M. Lucia, E. Baldwin, G. Ulbricht, et. al.
Wed, 13 Apr 22
64/73

Comments: 8 pages, 7 figures, SPIE Proceedings

Nonlinear mechanisms in Al and Ti superconducting travelling-wave parametric amplifiers [CL]

Posted on by

http://arxiv.org/abs/2202.11656


The underlying nonlinear mechanisms behind the operation of travelling-wave parametric amplifiers (TWPAs) are important in determining their performance in terms of added noise, maximum gain, and bandwidth. We describe a method of characterising the underlying nonlinearity of a superconducting material in terms of its dissipative-reactive ratio and the response time of the underlying microscopic processes. We describe and calculate the different behaviour arising from the equilibrium supercurrent nonlinearity, which has low dissipation and fast response time, and the non-equilibrium heating nonlinearity, which has high dissipation and slow response time. We have fabricated TWPAs based on Al and Ti, and characterised their nonlinearities using our analysis. For both Al and Ti, the measured dissipative-reactive ratios and response times are quantitatively similar to predictions for the non-equilibrium heating nonlinearity. In line with this, we were able to obtain more than 20 dB of peak power gain, although only over a narrow bandwidth of a few kilohertz.

Read this paper on arXiv…

S. Zhao, S. Withington and C. Thomas
Thu, 24 Feb 22
42/52

Comments: N/A

Effect of medium on fundamental interactions in gravity and condensed matter [CL]

Posted on by

http://arxiv.org/abs/2202.07044


Recently, it was shown that the gravitational field undergoes exponential cutoff at large cosmological scales due to the presence of background matter. In this article, we demonstrate that there is a close mathematical analogy between this effect and the behavior of the magnetic field induced by a solenoid placed in a superconductor.

Read this paper on arXiv…

A. Zhuk and V. Shulga
Wed, 16 Feb 22
36/69

Comments: 8 pages, no figures

Impact of the superconductors properties on the measurement sensitivity of resonant-based axion detectors [CL]

Posted on by

http://arxiv.org/abs/2112.12775


Axions, hypothetical particles theorized to solve the strong CP-problem, are presently being considered as strong candidates as cold dark matter constituents. The signal power of resonant-based axion detectors, known as haloscopes, is directly proportional to their quality factor $Q$. In this paper, the impact of the use of superconductors in the performances of the haloscopes is studied by evaluating the obtainable $Q$. In particular, the surface resistance $R_s$ of NbTi, Nb$3$Sn, YBa$_2$Cu$_3$O${7-\delta}$ and FeSe${0.5}$Te${0.5}$ is computed in the frequency, magnetic field and temperature ranges of interest, starting from the measured vortex motion complex resistivity and screening lengths of these materials. From $R_s$ the quality factor $Q$ of a cylindrical haloscope with copper conical bases and superconductive lateral wall, operating with the TM${010}$ mode, is evaluated and used to perform a comparison of the performances of the different materials. Both YBa$_2$Cu$_3$O${7-\delta}$ and FeSe${0.5}$Te${0.5}$ are shown to improve the measurement sensitivity by almost an order of magnitude with respect to a whole Cu cavity, while NbTi is shown to be suitable only at lower frequencies (<10 GHz). Nb$_3$Sn can give an intermediate improvement in the whole spectrum of interest.

Read this paper on arXiv…

A. Alimenti, K. Torokhtii, D. Gioacchino, et. al.
Fri, 24 Dec 21
9/58

Comments: 15 pages, 5 figures, submitted to Instruments journal (published by MDPI)

Impact of the superconductors properties on the measurement sensitivity of resonant-based axion detectors [CL]

Posted on by

http://arxiv.org/abs/2112.12775


Axions, hypothetical particles theorized to solve the strong CP-problem, are presently being considered as strong candidates as cold dark matter constituents. The signal power of resonant-based axion detectors, known as haloscopes, is directly proportional to their quality factor $Q$. In this paper, the impact of the use of superconductors in the performances of the haloscopes is studied by evaluating the obtainable $Q$. In particular, the surface resistance $R_s$ of NbTi, Nb$3$Sn, YBa$_2$Cu$_3$O${7-\delta}$ and FeSe${0.5}$Te${0.5}$ is computed in the frequency, magnetic field and temperature ranges of interest, starting from the measured vortex motion complex resistivity and screening lengths of these materials. From $R_s$ the quality factor $Q$ of a cylindrical haloscope with copper conical bases and superconductive lateral wall, operating with the TM${010}$ mode, is evaluated and used to perform a comparison of the performances of the different materials. Both YBa$_2$Cu$_3$O${7-\delta}$ and FeSe${0.5}$Te${0.5}$ are shown to improve the measurement sensitivity by almost an order of magnitude with respect to a whole Cu cavity, while NbTi is shown to be suitable only at lower frequencies (<10 GHz). Nb$_3$Sn can give an intermediate improvement in the whole spectrum of interest.

Read this paper on arXiv…

A. Alimenti, K. Torokhtii, D. Gioacchino, et. al.
Fri, 24 Dec 21
10/58

Comments: 15 pages, 5 figures, submitted to Instruments journal (published by MDPI)

Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor and depairing current density [CL]

Posted on by

http://arxiv.org/abs/2110.00573


We investigate how a combination of a nonmagnetic-impurity scattering rate $\gamma$ and finite subgap states parametrized by Dynes $\Gamma$ affects various physical quantities relevant to to superconducting devices: kinetic inductance $L_k$, complex conductivity $\sigma$, surface resistance $R_s$, quality factor $Q$, and depairing current density $J_d$. All the calculations are based on the Eilenberger formalism of the BCS theory. We assume the device materials are extreme type-II $s$-wave superconductors. It is well known that the optimum impurity concentration ($\gamma/\Delta_0 \sim 1$) minimizes $R_s$. Here, $\Delta_0$ is the pair potential for the idealized ($\Gamma\to 0$) superconductor for the temperature $T\to 0$. We find the optimum $\Gamma$ can also reduce $R_s$ by one order of magnitude for a clean superconductor ($\gamma/\Delta_0 < 1$) and a few tens $\%$ for a dirty superconductor ($\gamma/\Delta_0 > 1$). Also, we find a nearly-ideal ($\Gamma/\Delta_0 \ll 1$) clean-limit superconductor exhibits a frequency-independent $R_s$ for a broad range of frequency $\omega$, which can significantly improve $Q$ of a very compact cavity with a few tens of GHz frequency. As $\Gamma$ or $\gamma$ increases, the plateau disappears, and $R_s$ obeys the $\omega^2$ dependence. The subgap-state-induced residual surface resistance $R_{\rm res}$ is also studied, which can be detected by an SRF-grade high-$Q$ 3D resonator. We calculate $L_k(\gamma, \Gamma,T)$ and $J_d(\gamma, \Gamma,T)$, which are monotonic increasing and decreasing functions of $(\gamma, \Gamma,T)$, respectively. Measurements of $(\gamma, \Gamma)$ of device materials can give helpful information on engineering $(\gamma, \Gamma)$ via materials processing, by which it would be possible to improve $Q$, engineer $L_k$, and ameliorate $J_d$.

Read this paper on arXiv…

T. Kubo
Mon, 4 Oct 21
5/76

Comments: 15 pages, 15 figures

Directional Detection of Light Dark Matter in Superconductors [CL]

Posted on by

http://arxiv.org/abs/2109.04473


Superconducting detectors have been proposed as outstanding targets for the direct detection of light dark matter scattering at masses as low as a keV. We study the prospects for directional detection of dark matter in isotropic superconducting targets from the angular distribution of excitations produced in the material. We find that dark matter scattering produces initial excitations with an anisotropic distribution, and further show that this directional information can be preserved as the initial excitations relax. Our results demonstrate that directional detection is possible for a wide range of dark matter masses, and pave the way for light dark matter discovery with bulk superconducting targets.

Read this paper on arXiv…

Y. Hochberg, E. Kramer, N. Kurinsky, et. al.
Mon, 13 Sep 21
33/52

Comments: 5 pages + references, 2 figures. Includes supplementary material (11 pages, 5 figures). Code available at this https URL

Josephson junction formed in the wormhole space time from the analysis for the critical temperature of BEC [CL]

Posted on by

http://arxiv.org/abs/2108.08030


In this study, considering some gas in the Morris and Thorne’s traversable wormhole space time, we analyze its critical temperature of the Bose-Einstein condensate in the vicinity of its throat. As a result, we obtain the result that it is zero. Then, from this result, we point out that an analogues state to the Josephson junction is always formed at any temperatures except for zero in the vicinity of its throat. This would be interesting as a universal gravitational phenomenology.

Read this paper on arXiv…

S. Takeuchi
Thu, 19 Aug 21
45/54

Comments: 25 pages, 3 figures

Strong Negative Electrothermal Feedback in Thermal Kinetic Inductance Detectors [CL]

Posted on by

http://arxiv.org/abs/2107.12493


We demonstrate strong negative electrothermal feedback accelerating and linearizing the response of a thermal kinetic inductance detector (TKID). TKIDs are a proposed highly multiplexable replacement to transition-edge sensors and measure power through the temperature-dependent resonant frequency of a superconducting microresonator bolometer. At high readout probe power and probe frequency detuned from the TKID resonant frequency, we observe electrothermal feedback loop gain up to $\mathcal L$ $\approx$ 16 through measuring the reduction of settling time. We also show that the detector response has no detectable non-linearity over a 38% range of incident power and that the noise-equivalent power is below the design photon noise.

Read this paper on arXiv…

S. Agrawal, B. Steinbach, J. Bock, et. al.
Wed, 28 Jul 21
4/68

Comments: 8 pages, 9 figures, The following article has been submitted to the Journal of Applied Physics. After it is published, it will be found at this https URL

Microscopic description of axisymmetric vortices in $^{3}P_{2}$ superfluids [CL]

Posted on by

http://arxiv.org/abs/1908.06215


We study quantized vortices in ${}^{3}P_{2}$ superfluids using a microscopic theory for the first time. The theory is based on the Eilenberger equation to determine the order parameters and the Bogoliubov-de Gennes (BdG) equation to obtain the eigenenergies and the core magnetization. Within axisymmetric vortex configurations, we find several stable and metastable vortex configurations which depend on the strength of a magnetic field, similar to a $v$ vortex and $o$ vortex in $^3$He superfluids. We demonstrate that the $o$ vortex is the most stable axisymmetric vortex in the presence of a strong magnetic field, and we find two zero-energy Majorana fermion bound states in the $o$-vortex core. We show that the profiles of the core magnetization calculated using the BdG equation are drastically different from those calculated using only the order parameter profiles known before.

Read this paper on arXiv…

Y. Masaki, T. Mizushima and M. Nitta
Wed, 7 Jul 21
27/58

Comments: 15 pages, 8 figures

Non-Abelian Half-Quantum Vortices in ${}^{3}P_{2}$ Topological Superfluids [CL]

Posted on by

http://arxiv.org/abs/2107.02448


The existence and stability of non-Abelian half-quantum vortices (HQVs) are established in ${}^{3}P_{2}$ superfluids in neutron stars with strong magnetic fields, the largest topological quantum matter in our Universe. Using a self-consistent microscopic framework, we find that one integer vortex is energetically destabilized into a pair of two non-Abelian HQVs due to the strong spin-orbit coupled gap functions. We find a topologically protected Majorana fermion on each HQV, thereby providing two-fold non-Abelian anyons characterized by both Majorana fermions and a non-Abelian first homotopy group.

Read this paper on arXiv…

Y. Masaki, T. Mizushima and M. Nitta
Wed, 7 Jul 21
45/58

Comments: 6 pages, 4 figures

Condensate formation in collisionless plasma [CL]

Posted on by

http://arxiv.org/abs/2105.11212


Particle condensates in general magnetic mirror geometries in high temperature plasma may be caused by a discrete resonance with thermal ion-acoustic background noise near mirror points. The resonance breaks the bounce symmetry, temporally locking the particles to the resonant wavelength. The relevant correlation length is the ion gyroradius applying to all particles with mirror points distributed along it.

Read this paper on arXiv…

R. Treumann and W. Baumjohann
Tue, 25 May 21
68/75

Comments: 11 pages, no figures

Does our universe conform with the existence of a universal maximum energy-density $ρ^{uni}_{max}$ ? [GA]

Posted on by

http://arxiv.org/abs/2104.06321


Recent astronomical observations of high redshift quasars, dark matter-dominated galaxies, mergers of neutron stars, glitch phenomena in pulsars, cosmic microwave background and experimental data from hadronic colliders do not rule out, but they even support the hypothesis that the energy-density in our universe most likely is upper-limited by $\rho^{uni}{max},$ which is predicted to lie between $2$ to $3$ the nuclear density $\rho_0.$ Quantum fluids in the cores of massive NSs with $\rho \approx \rho^{uni}{max}$ reach the maximum compressibility state, where they become insensitive to further compression by the embedding spacetime and undergo a phase transition into the purely incompressible gluon-quark superfluid state. A direct correspondence between the positive energy stored in the embedding spacetime and the degree of compressibility and superfluidity of the trapped matter is proposed. In this paper relevant observation signatures that support the maximum density hypothesis are reviewed, a possible origin of $\rho^{uni}_{max}$ is proposed and finally the consequences of this scenario on the spacetime’s topology of the universe as well as on the mechanisms underlying the growth rate and power of the high redshift QSOs are discussed.

Read this paper on arXiv…

A. Hujeirat
Wed, 14 Apr 2021
60/67

Comments: 20 pages, 6 figures

Phonon-trapping enhanced energy resolution in superconducting single photon detectors [IMA]

Posted on by

http://arxiv.org/abs/2103.06723


A noiseless, photon counting detector, which resolves the energy of each photon, could radically change astronomy, biophysics and quantum optics. Superconducting detectors promise an intrinsic resolving power at visible wavelengths of $R=E/\delta E\approx100$ due to their low excitation energy. We study superconducting energy-resolving Microwave Kinetic Inductance Detectors (MKIDs), which hold particular promise for larger cameras. A visible/near-infrared photon absorbed in the superconductor creates a few thousand quasiparticles through several stages of electron-phonon interaction. Here we demonstrate experimentally that the resolving power of MKIDs at visible to near-infrared wavelengths is limited by the loss of hot phonons during this process. We measure the resolving power of our aluminum-based detector as a function of photon energy using four lasers with wavelengths between $1545-402$ nm. For detectors on thick SiN/Si and sapphire substrates the resolving power is limited to $10-21$ for the respective wavelengths, consistent with the loss of hot phonons. When we suspend the sensitive part of the detector on a 110 nm thick SiN membrane, the measured resolving power improves to $19-52$ respectively. The improvement is equivalent to a factor $8\pm2$ stronger phonon trapping on the membrane, which is consistent with a geometrical phonon propagation model for these hot phonons. We discuss a route towards the Fano limit by phonon engineering.

Read this paper on arXiv…

P. Visser, S. Rooij, V. Murugesan, et. al.
Fri, 12 Mar 21
29/59

Comments: 14 pages, 8 figures, including appendices

Characterization of a flux-driven Josephson parametric amplifier with near quantum-limited added noise for axion search experiments [CL]

Posted on by

http://arxiv.org/abs/2101.08496


The axion, a hypothetical elementary pseudoscalar, is expected to solve the strong CP problem of QCD and is also a promising candidate for dark matter. The most sensitive axion search experiments operate at millikelvin temperatures and hence rely on instrumentation that carries signals from a system at cryogenic temperatures to room temperature instrumentation. One of the biggest limiting factors affecting the parameter scanning speed of these detectors is the noise added by the components in the signal detection chain. Since the first amplifier in the chain limits the minimum noise, low-noise amplification is of paramount importance. This paper reports on the operation of a flux-driven Josephson parametric amplifier (JPA) operating at around 2.3 GHz with added noise approaching the quantum limit. The JPA was employed as a first stage amplifier in an experimental setting similar to the ones used in haloscope axion detectors. By operating the JPA at a gain of 19 dB and cascading it with two cryogenic amplifiers operating at 4 K, noise temperatures as low as 120 mK were achieved for the whole signal detection chain.

Read this paper on arXiv…

&. Kutlu, A. Loo, S. Uchaikin, et. al.
Fri, 22 Jan 21
38/69

Comments: N/A

Sensitive Superconducting Calorimeters for Dark Matter Search [CL]

Posted on by

http://arxiv.org/abs/2101.08558


The composition of dark matter is one of the puzzling topics in astrophysics. Since, the existence of axions would fill this gap of knowledge, several experiments for the search of axions have been designed in the last twenty years. Among all the others, light shining through walls experiments promise to push the exclusion limits to lower energies. To this end, effort is put for the development of single-photon detectors operating at frequencies $<100$ Ghz. Here, we review recent advancements in superconducting single-photon detection. In particular, we present two sensors based on one-dimensional Josephson junctions with the capability to be in situ tuned by simple current bias: the nanoscale transition edge sensor (nano-TES) and the Josephson escape sensor (JES). These two sensors seem to be the perfect candidates for the realization of microwave light shining through walls (LSW) experiments, since they show unprecedented frequency resolutions of about 100 GHz and 2 GHz for the nano-TES and JES, respectively.

Read this paper on arXiv…

F. Paolucci and F. Giazotto
Fri, 22 Jan 21
67/69

Comments: 15 pages, 7 figures. arXiv admin note: text overlap with arXiv:2011.08745

Simulating the radiation loss of superconducting submillimeter wave filters and transmission lines using Sonnet EM [IMA]

Posted on by

http://arxiv.org/abs/2012.07251


Superconducting resonators and transmission lines are fundamental building blocks of integrated circuits for millimeter-submillimeter astronomy. Accurate simulation of radiation loss from the circuit is crucial for the design of these circuits because radiation loss increases with frequency, and can thereby deteriorate the system performance. Here we show a stratification for a 2.5-dimensional method-of-moment simulator Sonnet EM that enables accurate simulations of the radiative resonant behavior of submillimeter-wave coplanar resonators and straight coplanar waveguides (CPWs). The Sonnet simulation agrees well with the measurement of the transmission through a coplanar resonant filter at 374.6 GHz. Our Sonnet stratification utilizes artificial lossy layers below the lossless substrate to absorb the radiation, and we use co-calibrated internal ports for de-embedding. With this type of stratification, Sonnet can be used to model superconducting millimeter-submillimeter wave circuits even when radiation loss is a potential concern.

Read this paper on arXiv…

A. Endo, A. Laguna, S. Hähnle, et. al.
Tue, 15 Dec 20
48/136

Comments: Presented at the SPIE Astronomical Telescopes + Instrumentation 2020. Full published paper, poster and video available at this https URL

Characterization of low-loss hydrogenated amorphous silicon films for superconducting resonators [IMA]

Posted on by

http://arxiv.org/abs/2012.07692


Superconducting resonators used in millimeter-submillimeter astronomy would greatly benefit from deposited dielectrics with a small dielectric loss. We deposited hydrogenated amorphous silicon films using plasma-enhanced chemical vapor deposition, at substrate temperatures of 100\deg C, 250\deg C and 350\deg C. The measured void volume fraction, hydrogen content, microstructure parameter, and bond-angle disorder are negatively correlated with the substrate temperature. All three films have a loss tangent below $10^{-5}$ for a resonator energy of $10^5$ photons, at 120 mK and 4-7 GHz. This makes these films promising for microwave kinetic inductance detectors and on-chip millimeter-submilimeter filters.

Read this paper on arXiv…

B. Buijtendorp, J. Bueno, D. Thoen, et. al.
Tue, 15 Dec 20
51/136

Comments: Presented at the SPIE Astronomical Telescopes + Instrumentation 2020. Full published paper, poster and video available at this https URL

Simulating the radiation loss of superconducting submillimeter wave filters and transmission lines using Sonnet EM [IMA]

Posted on by

http://arxiv.org/abs/2012.07251


Superconducting resonators and transmission lines are fundamental building blocks of integrated circuits for millimeter-submillimeter astronomy. Accurate simulation of radiation loss from the circuit is crucial for the design of these circuits because radiation loss increases with frequency, and can thereby deteriorate the system performance. Here we show a stratification for a 2.5-dimensional method-of-moment simulator Sonnet EM that enables accurate simulations of the radiative resonant behavior of submillimeter-wave coplanar resonators and straight coplanar waveguides (CPWs). The Sonnet simulation agrees well with the measurement of the transmission through a coplanar resonant filter at 374.6 GHz. Our Sonnet stratification utilizes artificial lossy layers below the lossless substrate to absorb the radiation, and we use co-calibrated internal ports for de-embedding. With this type of stratification, Sonnet can be used to model superconducting millimeter-submillimeter wave circuits even when radiation loss is a potential concern.

Read this paper on arXiv…

A. Endo, A. Laguna, S. Hähnle, et. al.
Tue, 15 Dec 20
59/136

Comments: Presented at the SPIE Astronomical Telescopes + Instrumentation 2020. Full published paper, poster and video available at this https URL

Anomalous Frequency Noise from the Megahertz Channelizing Resonators in Frequency-Division Multiplexed Transition Edge Sensor Readout [IMA]

Posted on by

http://arxiv.org/abs/2012.07077


Superconducting lithographed resonators have a broad range of current and potential applications in the multiplexed readout of cryogenic detectors. Here, we focus on LC bandpass filters with resonances in the 1-5 MHz range used in the transition edge sensor (TES) bolometer readout of the Simons Array cosmic microwave background (CMB) experiment. In this readout scheme, each detector signal amplitude-modulates a sinusoidal carrier tone at the resonance frequency of the detector’s accompanying LC filter. Many modulated signals are transmitted over the same wire pair, and quadrature demodulation recovers the complex detector signal. We observe a noise in the resonant frequencies of the LC filters, which presents primarily as a current-dependent noise in the quadrature component after demodulation. This noise has a rich phenomenology, bearing many similarities to that of two-level system (TLS) noise observed in similar resonators in the GHz regime. These similarities suggest a common physical origin, thereby offering a new regime in which the underlying physics might be probed. We further describe an observed non-orthogonality between this noise and the detector responsivities, and present laboratory measurements that bound the resulting sensitivity penalty expected in the Simons Array. From these results, we do not anticipate this noise to appreciably affect the overall Simons Array sensitivity, nor do we expect it to limit future implementations.

Read this paper on arXiv…

J. Groh, K. Arnold, J. Avva, et. al.
Tue, 15 Dec 20
114/136

Comments: 5 pages, 5 figures, submitted to IEEE Transactions on Applied Superconductivity

Sub-gap kinetic inductance detector sensitive to 85 GHz radiation [CL]

Posted on by

http://arxiv.org/abs/2010.03845


We have fabricated an array of Sub-gap Kinetic Inductance Detectors (SKIDs) made of granular aluminum ($T_c\sim$2~K) sensitive in the 80-90 GHz frequency band and operating at 300~mK. We measured a noise equivalent power of $1.3\times10^{-16}$~W/Hz$^{0.5}$ on average and $2.6\times10^{-17}$~W/Hz$^{0.5}$ at best, for an illuminating power of 50~fW per pixel. Even though the circuit design of SKIDs is identical to that of the Kinetic Inductance Detectors (KIDs), the SKIDs operating principle is based on their sensitivity to sub-gap excitations. This detection scheme is advantageous because it avoids having to lower the operating temperature proportionally to the lowest detectable frequency. The SKIDs presented here are intrinsically selecting the 80-90 GHz frequency band, well below the superconducting spectral gap of the film, at approximately 180 GHz.

Read this paper on arXiv…

F. Levy-Bertrand, A. Benoît, O. Bourrion, et. al.
Fri, 9 Oct 20
19/64

Comments: Suggestions and comments are welcome

Superfluid vortex-mediated mutual friction in non-homogeneous neutron star interiors [HEAP]

Posted on by

http://arxiv.org/abs/2007.11720


Understanding the average motion of a multitude of superfluid vortices in the interior of a neutron star is a key ingredient for most theories of pulsar glitches. In this paper we propose a kinetic approach to compute the mutual friction force that is responsible for the momentum exchange between the normal and superfluid components in a neutron star, where the mutual friction is extracted from a suitable average over the motion of many vortex lines. As a first step towards a better modelling of the repinning and depinning processes of many vortex lines in a neutron star, we consider here only straight and non-interacting vortices: we adopt a minimal model for the dynamics of an ensemble of point vortices in two dimensions immersed in a non-homogeneous medium that acts as a pinning landscape. Since the degree of disorder in the inner crust or outer core of a neutron star is unknown, we compare the two possible scenarios of periodic and disordered pinscapes. This approach allows to extract the mutual friction between the superfluid and the normal component in the star when, in addition to the usual Magnus and drag forces acting on vortex lines, also a pinning force is at work. The effect of disorder on the depinning transition is also discussed.

Read this paper on arXiv…

M. Antonelli and B. Haskell
Fri, 24 Jul 20
-512/53

Comments: 17 pages, 10 figures

Searching for low mass dark matter via phonon creation in superfluid 4He [CL]

Posted on by

http://arxiv.org/abs/2005.08824


We consider the scattering of dark matter particles from superfluid liquid $^4$He, which has been proposed as a target for their direct detection. Focusing on dark matter masses below ~1 MeV, we demonstrate from sum-rule arguments that for momentum transfers of interest the dominant process is the creation of a single phonon, with the direct creation of two or more phonons much less likely. We show further that the anomalous dispersion of phonons in liquid $^4$He at low pressures [i.e., $d^2\omega (q)/dq^2 > 0$, where $q$ and $\omega(q)$ are the phonon momentum and energy] has the important consequence that a single phonon will decay over a relatively short distance into a shower of lower energy phonons centered on the direction of the original phonon. Thus the experimental challenge in this regime is to detect a shower of low energy phonons, not just a single phonon. Additional information from the distribution of phonons in such a shower could enhance the determination of the dark matter mass.

Read this paper on arXiv…

G. Baym, D. Beck, J. Filippini, et. al.
Tue, 19 May 20
55/92

Comments: 17 pages, 12 figures

Superconducting Materials for Microwave Kinetic Inductance Detectors [IMA]

Posted on by

http://arxiv.org/abs/2004.14576


The superconducting materials that make up an MKID have a significant effect on its performance. The $T_\textrm{c}$ and normal state resistivity $\rho_\textrm{N}$ of the film determine the penetration depth $\lambda$ and therefore how much kinetic inductance it has. The ratio of kinetic inductance to total inductance ($\alpha$), the volume of the inductor, and $Q_\textrm{m}$ determines the magnitude of the response to incoming energy. The quasiparticle lifetime $\tau_\textrm{qp}$ is the characteristic time during which the MKID’s surface impedance is modified by the incoming energy. Many materials have been explored for use in superconducting resonators and MKIDs, but that information is often not published or scattered around the literature. This chapter contains information and references on the work that has been done with thin film lithographed circuits for MKIDs over the last two decades. Note that measured material properties such as the internal loss quality factor $Q_\textrm{i}$ and quasiparticle lifetime $\tau_\textrm{qp}$ vary significantly depending on how the MKID superconducting thin film is made and the system they are measured in, so it is best to interpret all stated values as typical but not definitive. Values are omitted in cases when there aren’t enough measurements or there is too much disagreement in the literature to estimate a typical value. In order to be as complete as possible some unpublished results from the author’s lab are included and can be identified by the lack of a reference. Unless noted all films are polycrystalline or amorphous.

Read this paper on arXiv…

B. Mazin
Fri, 1 May 20
16/54

Comments: 19 pages, 4 figures. To appear in the Handbook of Superconducting Materials

Coexistence phase of $^{1}S_{0}$ and $^{3}P_{2}$ superfluids in neutron stars [CL]

Posted on by

http://arxiv.org/abs/2002.05429


In neutron star matter, there exist $^{1}S_{0}$ superfluids in lower density in the crust while $^{3}P_{2}$ superfluids are believed to exist at higher density deep inside the core. In the latter, depending on the temperature and magnetic field, either uniaxial nematic (UN) phase, D${2}$-biaxial nematic (D${2}$-BN) phase, or D${4}$-biaxial nematic (D${4}$-BN) phase appears. In this paper, we discuss a mixture of the $^{1}S_{0}$ and $^{3}P_{2}$ superfluids and find their coexistence. Adopting the loop expansion and the weak-coupling approximation for the interaction between two neutrons, we obtain the Ginzburg-Landau (GL) free energy in which both of the $^{1}S_{0}$ and $^{3}P_{2}$ condensates are taken into account by including the coupling terms between them. We analyze the GL free energy and obtain the phase diagram for the temperature and magnetic field. We find that the $^{1}S_{0}$ superfluid excludes the $^{3}P_{2}$ superfluid completely in the absence of magnetic field, they can coexist for weak magnetic fields, and the $^{1}S_{0}$ superfluid is expelled by the $^{3}P_{2}$ superfluid at strong magnetic fields, thereby proving the robustness of $^{3}P_{2}$ superfluid against the magnetic field. We further show that the D${4}$-BN phase covers the whole region of the $^{3}P{2}$ superfluidity as a result of the coupling term, in contrast to the case of a pure $^{3}P_{2}$ superfluid studied before in which the D${4}$-BN phase is realized only under strong magnetic fields. Thus, the D${4}$-BN phase is topologically most interesting phase, e.g., admitting half-quantized non-Abelian vortices relevant not only in magnetars but also in ordinary neutron stars.

Read this paper on arXiv…

S. Yasui, D. Inotani and M. Nitta
Fri, 14 Feb 20
17/51

Comments: 14 pages, 3 figures

Superfluidity in Disordered Neutron Stars Crusts [HEAP]

Posted on by

http://arxiv.org/abs/2001.09959


Nonequilibrium conditions imposed by neutrino cooling through the liquid-solid transition lead to disorder in the solid crust of neutron stars. Disorder reduces the superfluid fraction, $\rho_s/\rho$, at densities above that of neutron drip, $\rho_d \approx 4\times 10^{11}\,g/cm^3$. For an amorphous solid crust the suppression of $\rho_s$ is small, except in the highest density regions of the crust. In contrast to the strong reduction in neutron conduction predicted for coherent Bragg scattering in a crystalline crust, the disordered solid crust supports sufficient neutron superfluid density to account for pulsar glitches.

Read this paper on arXiv…

J. Sauls, N. Chamel and M. Alpar
Tue, 28 Jan 20
19/63

Comments: 6 pages, 5 figures

Nonlinear Effects in Superconducting Thin Film Microwave Resonators [CL]

Posted on by

http://arxiv.org/abs/2001.02540


We discuss how reactive and dissipative non-linearities affect the intrinsic response of superconducting thin-film resonators. We explain how most, if not all, of the complex phenomena commonly seen can be described by a model in which the underlying resonance is a single-pole Lorentzian, but whose centre frequency and quality factor change as external parameters, such as readout power and frequency, are varied. What is seen during a vector-network-analyser measurement is series of samples taken from an ideal Lorentzian that is shifting and spreading as the readout frequency is changed. According to this model, it is perfectly proper to refer to, and measure, the resonant frequency and quality factor of the underlying resonance, even though the swept-frequency curves appear highly distorted and hysteretic. In those cases where the resonance curve is highly distorted, the specific shape of the trajectory in the Argand plane gives valuable insights into the second-order physical processes present. We discuss the formulation and consequences of this approach in the case of non-linear kinetic inductance, two-level-system loss, quasiparticle generation, and a generic model based on a power-law form. The generic model captures the key features of specific dissipative non-linearities, but additionally leads to insights into how general dissipative processes create characteristic forms in the Argand plane. We provide detailed formulations in each case, and indicate how they lead to the wide variety of phenomena commonly seen in experimental data. We also explain how the properties of the underlying resonance can be extracted from this data. Overall, our paper provides a self-contained compendium of behaviour that will help practitioners interpret and determine important parameters from distorted swept-frequency measurements.

Read this paper on arXiv…

C. Thomas, S. Withington, Z. Sun, et. al.
Fri, 10 Jan 20
25/65

Comments: 55 pages, 15 figures

Simultaneous Noise and Impedance Fitting to Transition-Edge Sensor Data using Differential Evolution [IMA]

Posted on by

http://arxiv.org/abs/1909.05643


We discuss a robust method to simultaneously fit a complex model both to the complex impedance and the noise data for transition-edge sensors (TES). It is based on a differential evolution (DE) algorithm, providing accurate and repeatable results with only a small increase in computational cost compared to the standard least squares (LS) fitting method. Test fits are made using both DE and LS methods, and the results compared with previously determined best fits, with varying initial value deviations and limit ranges for the parameters. The robustness of DE is demonstrated with successful fits even when parameter limits up to a factor of 5 from the known values were used. It is shown that the least squares fitting becomes unreliable beyond a 10% deviation from the known values.

Read this paper on arXiv…

A. Helenius, T. Puurtinen, K. Kinnunen, et. al.
Fri, 13 Sep 19
3/70

Comments: N/A

Graphene-based Josephson junction microwave bolometer [CL]

Posted on by

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.

Read this paper on arXiv…

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

Comments: 8 pages, 4 figures

Towards 100,000-pixel microcalorimeter arrays using multi-absorber transition-edge sensors [IMA]

Posted on by

http://arxiv.org/abs/1908.02687


We report on the development of multi-absorber transition edge sensors (TESs), referred to as hydras. A hydra consists of multiple x-ray absorbers each with a different thermal conductance to a TES. Position information is encoded in the pulse shape. With some trade-off in performance, hydras enable very large format arrays without the prohibitive increase in bias and read-out components associated with arrays of individual TESs. Hydras are under development for the next generation of space telescope such as Lynx. Lynx is a NASA concept under study that will combine a < 1 arcsecond angular resolution optic with 100,000-pixel microcalorimeter array with energy resolution of deltaE_FWHM ~ 3 eV in the soft x-ray energy range. We present first results from hydras with 25-pixels for Lynx. Designs with absorbers on a 25 micron and 50 micron pitch are studied. Arrays incorporate, for the first time, microstrip buried wiring layers of suitable pitch and density required to readout a full-scale Lynx array. The resolution from the coadded energy histogram including all 25-pixels was deltaE_FWHM = 1.66+/-0.02 eV and 3.34+/-0.06 eV at an energy of 1.5 keV for the 25 micron and 50 micron absorber designs respectively. Position discrimination is demonstrated from parameterization of the rise-time.

Read this paper on arXiv…

S. Smith, J. Adams, S. Bandler, et. al.
Thu, 8 Aug 19
70/78

Comments: 7 pages, 5 figures. Low Temperature Detectors 18 Conference, Milan Italy

Towards 100,000-pixel microcalorimeter arrays using multi-absorber transition-edge sensors [IMA]

Posted on by

http://arxiv.org/abs/1908.02687


We report on the development of multi-absorber transition edge sensors (TESs), referred to as hydras. A hydra consists of multiple x-ray absorbers each with a different thermal conductance to a TES. Position information is encoded in the pulse shape. With some trade-off in performance, hydras enable very large format arrays without the prohibitive increase in bias and read-out components associated with arrays of individual TESs. Hydras are under development for the next generation of space telescope such as Lynx. Lynx is a NASA concept under study that will combine a < 1 arcsecond angular resolution optic with 100,000-pixel microcalorimeter array with energy resolution of deltaE_FWHM ~ 3 eV in the soft x-ray energy range. We present first results from hydras with 25-pixels for Lynx. Designs with absorbers on a 25 micron and 50 micron pitch are studied. Arrays incorporate, for the first time, microstrip buried wiring layers of suitable pitch and density required to readout a full-scale Lynx array. The resolution from the coadded energy histogram including all 25-pixels was deltaE_FWHM = 1.66+/-0.02 eV and 3.34+/-0.06 eV at an energy of 1.5 keV for the 25 micron and 50 micron absorber designs respectively. Position discrimination is demonstrated from parameterization of the rise-time.

Read this paper on arXiv…

S. Smith, J. Adams, S. Bandler, et. al.
Thu, 8 Aug 19
27/78

Comments: 7 pages, 5 figures. Low Temperature Detectors 18 Conference, Milan Italy

Superconducting nanowires as high-rate photon detectors in strong magnetic fields [CL]

Posted on by

http://arxiv.org/abs/1907.13059


Superconducting nanowire single-photon detectors are capable of single-photon detection across a large spectral range, with near-unity detection efficiency, picosecond timing jitter, and sub-10 $\mu$m position resolution at rates as high as 1 GHz. In an effort to bring this technology into nuclear physics experiments, we fabricate Niobium Nitride nanowire detectors using novel material preparation methods and test their performance in strong magnetic fields. We demonstrate that these devices are capable of detection of 400 nm wavelength photons with saturated internal quantum efficiency at liquid helium temperatures and in magnetic fields up to 8 T at high rates and with nearly zero dark counts.

Read this paper on arXiv…

T. Polakovic, W. Armstrong, V. Yefremenko, et. al.
Wed, 31 Jul 19
25/65

Comments: N/A

Superfluidity in the Interiors of Neutron Stars [HEAP]

Posted on by

http://arxiv.org/abs/1906.09641


I review some of the ideas that have been proposed for the structure of neutron star interiors, and concentrate on the theoretical arguments for the existence of superfluidity in neutron stars. I also discuss the implications of neutron superfluidity and proton superconductivity for the rotational dynamics of pulsars, and review arguments that have been proposed for observable effects of superfluidity on the timing history of pulsars and perhaps other neutron stars. The Lecture notes also include discussions of several features that are unique to interacting superfluid-superconducting mixtures, as well as the magnetic structure of quantized vortices in spin-triplet ($^3$P$_2$) neutron superfluids.

Read this paper on arXiv…

J. Sauls
Tue, 25 Jun 19
15/68

Comments: Original manuscript (34 pages, 8 figures), with minor typographical corrections, of my Lecture Notes for the NATO Advanced Study Institute on “Timing Neutron Stars”, held in Cesme, Turkey, April 4-15, 1988

Superfluid Phase Transitions and Effects of Thermal Pairing Fluctuations in Asymmetric Nuclear Matter [CL]

Posted on by

http://arxiv.org/abs/1906.02098


We investigate superfluid phase transitions of asymmetric nuclear matter at finite temperature ($T$) and density ($\rho$) with a low proton fraction ($Y_{\rm p} \le 0.2$) which is relevant to the inner crust and outer core of neutron stars. A strong-coupling theory developed for two-component atomic Fermi gases is generalized to the four-component case and is applied to the system of spin-$1/2$ neutrons and protons. The empirical phase shifts of neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) interactions up to $k = 2$ ${\rm fm}^{-1}$ are described by multi-rank separable potentials. We show that (i) the critical temperature of the neutron superfluidity $T_{\rm c}^{\rm nn}$ at $Y_{\rm p}=0$ agrees well with Monte Carlo data at low densities and takes a maximum value $T_{\rm c}^{\rm nn}=1.68$ MeV at $\rho/\rho_0 = 0.14$ with $\rho_0=0.17$ fm$^{-3}$, (ii) the critical temperature of the proton superconductivity $T_{\rm c}^{\rm pp}$ for $Y_{\rm p} \le 0.2$ is substantially suppressed at low densities due to np-pairing fluctuations and starts to dominate over $T_{\rm c}^{\rm nn}$ only above $\rho/\rho_0 = 0.70$ $(0.77)$ for $Y_p =0.1$ $(0.2)$, and (iii) the deuteron condensation temperature $T_{\rm c}^{\rm d}$ is suppressed at $Y_{\rm p}\le 0.2$ due to the large mismatch of the two Fermi surfaces.

Read this paper on arXiv…

H. Tajima, T. Hatsuda, P. Wyk, et. al.
Thu, 6 Jun 19
26/67

Comments: 23 pages, 12 figures

Symmetry and topology of the boundary of neutron $^{3}P_{2}$ superfluids in neutron stars: boojums as surface topological defects [CL]

Posted on by

http://arxiv.org/abs/1905.13666


We study surface effects of neutron $^{3}P_{2}$ superfluids in neutron stars. $^{3}P_{2}$ superfluids are in uniaxial nematic (UN), D${2}$ biaxial nematic (BN), or D${4}$ BN phase, depending on the strength of magnetic fields from small to large. We suppose a neutron $^{3}P_{2}$ superfluid in a ball facing to the boundary at the surface sphere. Adopting a suitable boundary condition for $^{3}P_{2}$ condensates, we solve the Ginzburg-Landau equation to find several surface properties for the neutron $^{3}P_{2}$ superfluid. First, the phase on the surface can be different from that of the bulk, and symmetry restoration/breaking occurs in general on the surface. Second, the distribution of the surface energy density has an anisotropy depending on the polar angle in the sphere, which may lead to the deformation of the geometrical shape of the surface. Third, the order parameter manifold (OPM) induced on the surface, which is described by two-dimensional vector fields induced on the surface from the condensates, allows topological defects (vortices) on the surface, and there must exist such defects even in the ground state thanks to the Poincar\'{e}-Hopf theorem: although the numbers of the vortices and anti-vortices depend on the bulk phases, the difference between them are topologically invariant (the Euler number $\chi=2$) irrespective to the bulk phases. These vortices which are not extended to the bulk are called boojums in the context of liquid crystals and helium-3 superfluids. The surface properties of the neutron $^{3}P_{2}$ superfluid found in this paper may provide us useful information to study neutron stars.

Read this paper on arXiv…

S. Yasui, C. Chatterjee and M. Nitta
Mon, 3 Jun 19
2/59

Comments: 30 pages, 11 figures

Revisiting Ginzburg-Landau theory for neutron $^3P_2$ superfluidity in neutron stars [CL]

Posted on by

http://arxiv.org/abs/1904.11399


The Ginzburg-Landau (GL) effective theory is a useful tool to study a superconductivity or superfluidity near the critical temperature, and usually the expansion up to the 4th order in terms of order parameters is sufficient for the description of the second-order phase transition. In this paper, we discuss the GL equation for the neutron $^{3}P_{2}$ superfluidity relevant for interior of neutron stars. We derive the GL expansion up to the 8th order in the condensates and find that this order is necessary for the system to have the unique ground state, unlike the ordinary cases. Starting from the $LS$ potential, which provides the dominant attraction between two neutrons at the high density, we derive the GL equation in the path-integral formalism, where the auxiliary field method and the Nambu-Gor’kov representation are used. We present the detailed description for the trace calculation necessary in the derivation of the GL equation. As numerical results, we show the phase diagram of the neutron $^{3}P_{2}$ superfluidity on the plane spanned by the temperature and magnetic field, and find that the 8th order terms lead to a first-order phase transition, whose existence was predicted in the Bogoliubov-de Gennes equation but has not been found thus far within the framework of the GL expansion up to the 6th order. The first-order phase transition will affect the interior structures inside the neutron stars.

Read this paper on arXiv…

S. Yasui, C. Chatterjee, M. Kobayashi, et. al.
Fri, 26 Apr 19
62/69

Comments: 23 pages, 3 figures

Kinetic Inductance Detectors and readout electronics for the OLIMPO experiment [IMA]

Posted on by

http://arxiv.org/abs/1904.01890


Kinetic Inductance Detectors (KIDs) are superconductive low$-$temperature detectors useful for astrophysics and particle physics. We have developed arrays of lumped elements KIDs (LEKIDs) sensitive to microwave photons, optimized for the four horn-coupled focal planes of the OLIMPO balloon-borne telescope, working in the spectral bands centered at 150 GHz, 250 GHz, 350 GHz, and 460 GHz. This is aimed at measuring the spectrum of the Sunyaev-Zel’dovich effect for a number of galaxy clusters, and will validate LEKIDs technology in a space-like environment. Our detectors are optimized for an intermediate background level, due to the presence of residual atmosphere and room–temperature optical system and they operate at a temperature of 0.3 K. The LEKID planar superconducting circuits are designed to resonate between 100 and 600 MHz, and to match the impedance of the feeding waveguides; the measured quality factors of the resonators are in the $10^{4}-10^{5}$ range, and they have been tuned to obtain the needed dynamic range. The readout electronics is composed of a $cold$ $part$, which includes a low noise amplifier, a dc$-$block, coaxial cables, and power attenuators; and a $room-temperature$ $part$, FPGA$-$based, including up and down-conversion microwave components (IQ modulator, IQ demodulator, amplifiers, bias tees, attenuators). In this contribution, we describe the optimization, fabrication, characterization and validation of the OLIMPO detector system.

Read this paper on arXiv…

A. Paiella, E. Battistelli, M. Castellano, et. al.
Thu, 4 Apr 19
17/68

Comments: Proceedings of WOLTE13, September 10-13, 2018 Sorrento, Italy

Force on proton vortices in superfluid neutron stars [HEAP]

Posted on by

http://arxiv.org/abs/1904.01363


Force on proton vortices in superfluid and superconducting matter of neutron stars is calculated at vanishing stellar temperature. Both longitudinal (dissipative) and transverse (Lorentz-type) components of the force are derived in a coherent way and compared in detail with the corresponding expressions available in the literature. This allows us to resolve a controversy about the form of the Lorentz-type force component acting on proton vortices. The calculated force is a key ingredient in magnetohydrodynamics of superconducting neutron stars and is important for modeling the evolution of stellar magnetic field.

Read this paper on arXiv…

M. Gusakov
Wed, 3 Apr 19
6/68

Comments: 16 pages, 8 figures, to be published in MNRAS

Effects of strong magnetic fields on neutron $^{3}P_{2}$ superfluidity in spin-orbit interactions [CL]

Posted on by

http://arxiv.org/abs/1902.00674


We discuss neutron $^{3}P_{2}$ phases in the core of neutron stars in strong magnetic field (magnetars). The neutron $^{3}P_{2}$ pairing provides a wide variety of condensates, such as the uniaxial nematic and (D${2}$ and D${4}$) biaxial nematic, with different symmetries stemming from the combinations of spin and momentum. Based on the spin-orbital angular momentum coupling and the spin-magnetic field coupling of the neutrons, we derive the Ginzburg-Landau equation containing higher order terms of the magnetic field. We investigate the phase diagram of the neutron $^{3}P_{2}$ superfluidity, and find that the D$_{2}$ biaxial nematic phase is extended by the higher order terms of the magnetic field. We also discuss the thermodynamic properties, the heat capacity and the spin susceptibility.

Read this paper on arXiv…

S. Yasui, C. Chatterjee and M. Nitta
Tue, 5 Feb 19
12/86

Comments: Prepared for proceedings of QNP-2018, “The 8th International Conference on Quarks and Nuclear Physics” to be published in JPS Conf. Proc. Based on the original paper arXiv:1810.04901 [nucl-th]

Degenerate Dark Matter at Galactic Scales: A BCS Theory [GA]

Posted on by

http://arxiv.org/abs/1811.00716


We show that if dark matter in a typical galaxy is a degenerate Fermi gas, particles should have a mass of $\sim$ 1eV for the galaxy to be stable. While this is the mass range of the active neutrinos, they are not a dark matter candidate in SM-GR-$\Lambda$-CDM. To show that the bounds on active neutrino dark matter are model dependent, we explore the predictions of SM-LGT cosmological model. First, primordial neutrinos are predicted to freeze-out non-relativistically at early universe without affecting the expansion rate. Second, they make a degenerate gas in galaxies at the present time. Third, SM-LGT Hamiltonian at low temperatures is identical with that of the BCS theory of superconductivity. Consequently, there exists a narrow band of compressible condensed bosonic bound states on top of the Fermi surface which forms some denser structures.

Read this paper on arXiv…

A. Borzou
Mon, 5 Nov 18
11/49

Comments: 8 pages, 3 figures

Two SQUID amplifiers intended to alleviate the summing node inductance problem in multiplexed arrays of Transition Edge Sensors [IMA]

Posted on by

http://arxiv.org/abs/1810.09122


Frequency Domain Multiplexed detector arrays constructed of superconducting Transition Edge Sensors in the current-summing configuration suffer from the finite impedance of the summing node which should ideally be zero. We suggest two circuits to alleviate the effect. The first circuit uses a capacitive resonant transformer to increase the voltages and decrease the currents of TES signals to overcome the parasitic inductance of the interconnections. On the SQUID chip impedance transform to the opposite direction takes place. The second circuit implements a power combiner having a better branch-to-branch isolation than a simple T-junction. Two SQUID devices have been designed and fabricated for a proof-of-principle demonstration of the circuits.

Read this paper on arXiv…

M. Kiviranta, L. Grönberg and J. Kuur
Tue, 23 Oct 18
58/69

Comments: 6 pages, 7 figures

Low-dissipating push-pull SQUID amplifier for TES detector readout [IMA]

Posted on by

http://arxiv.org/abs/1810.04706


We suggest SQUID amplifier configuration intended for millikelvin refrigerators where cooling power is limited and hence high power efficiency is desirable. The configuration operates the SQUIDs in class-AB rather than the traditional class-A. A proof-of principle demonstration at T = 4.2 K is presented.

Read this paper on arXiv…

M. Kiviranta
Fri, 12 Oct 18
20/59

Comments: 4 pages, 6 figures

Phase structure of neutron $^{3}P_{2}$ superfluids in strong magnetic fields in neutron stars [CL]

Posted on by

http://arxiv.org/abs/1810.04901


We discuss the effect of strong magnetic field on neutron $^{3}P_{2}$ superfluidity. Based on the attraction in the $^{3}P_{2}$ pair of two neutrons, we derive the Ginzburg-Landau equation in the path integral formalism by adopting the bosonization technique and leave the next-to-leading order in the expansion of the magnetic field $B$. We determine the $(T,B)$ phase diagram with temperature $T$, comprising three phases: the uniaxial nematic (UN) phase for $B=0$, D${2}$-biaxial nematic (BN) and D${4}$-BN phases in the finite $B$ and strong $B$ such as magnetars, respectively, where D${2}$ and D${4}$ are dihedral groups. we find that, compared with the leading order in the magnetic field known before, the region of the D${2}$-BN phase in the $(T,B)$ plane is extended by the effect of the next-to-leading order terms of the magnetic field. We also present the thermodynamic properties, such as heat capacities and spin susceptibility, and find that the spin susceptibility is anisotropic in the D${2}$-BN phase and isotropic in the UN and D$_{4}$-BN phases. Those information will be useful to understand the internal structures of magnetars.

Read this paper on arXiv…

S. Yasui, C. Chatterjee and M. Nitta
Fri, 12 Oct 18
43/59

Comments: 11 pages, 3 figures

Increased multiplexing of superconducting microresonator arrays by post-characterization adaptation of the on-chip capacitors [IMA]

Posted on by

http://arxiv.org/abs/1808.03779


We present an interdigitated capacitor trimming technique for fine-tuning the resonance frequency of superconducting microresonators and increasing the multiplexing factor. We first measure the optical response of the array with a beam mapping system to link all resonances to their physical resonators. Then a new set of resonance frequencies with uniform spacing and higher multiplexing factor is designed. We use simulations to deduce the lengths that we should trim from the capacitor fingers in order to shift the resonances to the desired frequencies. The sample is then modified using contact lithography and re-measured using the same setup. We demonstrate this technique on a 112-pixel aluminum lumped-element kinetic-inductance detector array. Before trimming, the resonance frequency deviation of this array is investigated. The variation of the inductor width plays the main role for the deviation. After trimming, the mean fractional frequency error for identified resonators is -6.4e-4, with a standard deviation of 1.8e-4. The final optical yield is increased from 70.5% to 96.7% with no observable crosstalk beyond -15 dB during mapping. This technique could be applied to other photon-sensitive superconducting microresonator arrays for increasing the yield and multiplexing factor.

Read this paper on arXiv…

S. Shu, M. Calvo, J. Goupy, et. al.
Tue, 14 Aug 18
25/65

Comments: 5 pages, 4 figures, accepted by Applied Physical Letters

Quark-hadron continuity under rotation: vortex continuity or boojum? [CL]

Posted on by

http://arxiv.org/abs/1806.09291


Quark-hadron continuity was proposed as crossover between hadronic matter and quark matter without a phase transition, based on matching of symmetry and excitations in both phases. In the limit of light strange quark mass, it connects hyperon matter and color-flavor locked (CFL) phase exhibiting color superconductivity. Recently, this conjecture was proposed to be generalized in the presence of superfluid vortices penetrating the both phases in arXiv:1803.05115 [hep-ph], in which they suggested that one hadronic superfluid vortex in hyperon matter could be connected to one non-Abelian vortex (color magnetic flux tube) in the CFL phase. Here, we argue that their proposal is consistent only at large distances: Instead, we show that three hadronic superfluid vortices must join together to three non-Abelian vortices with different colors with the total color magnetic fluxes canceled out, where the junction was called a colorful boojum. We rigorously prove this both in a macroscopic theory based on the Ginzburg-Landau description, in which symmetry and excitations match including vortex cores, and a microscopic theory based on the Bogoliubov de-Gennes equation, in which the Aharanov-Bohm phase of quarks around vortices match.

Read this paper on arXiv…

C. Chatterjee, M. Nitta and S. Yasui
Tue, 26 Jun 18
45/71

Comments: 7 pages, 2 figures

Tunable sub-gap radiation detection with superconducting resonators [CL]

Posted on by

http://arxiv.org/abs/1802.10379


We have fabricated planar amorphous Indium Oxide superconducting resonators ($T_c\sim2.8$ K) that are sensitive to frequency-selective radiation in the range of 7 to 10 GHz. Those values lay far below twice the superconducting gap that worths about 200 GHz. The photons detection consists in a shift of the fundamental resonance frequency. We show that the detected frequency can be adjusted by modulating the total length of the superconducting resonator. We attribute those observations to the excitation of higher-order resonance modes. The coupling between the fundamental lumped and the higher order distributed resonance is due to the kinetic inductance non-linearity with current. These devices, that we have called Sub-gap Kinetic Inductance Detectors (SKIDs), are to be distinguished from the standard Kinetic Inductance Detectors (KIDs) in which quasi-particles are generated when incident light breaks down Cooper pairs.

Read this paper on arXiv…

O. Dupre, A. Calvo, A. Catalano, et. al.
Thu, 1 Mar 18
43/66

Comments: article: 6 pages, 4 figures supplementary: 1 page, 2 figures

Dynamical onset of superconductivity and retention of magnetic fields in cooling neutron stars [HEAP]

Posted on by

http://arxiv.org/abs/1711.08480


A superconductor of paired protons is thought to form in the core of neutron stars soon after their birth. Minimum energy conditions suggest magnetic flux is expelled from the superconducting region due to the Meissner effect, such that the neutron star core is largely devoid of magnetic fields for some nuclear equation of state and proton pairing models. We show via neutron star cooling simulations that the superconducting region expands faster than flux is expected to be expelled because cooling timescales are much shorter than timescales of magnetic field diffusion. Thus magnetic fields remain in the bulk of the neutron star core for at least 10^6-10^7 yr. We estimate the size of flux free regions at 10^7 yr to be <~ 100 m for a magnetic field of 10^11 G and possibly smaller for stronger field strengths. For proton pairing models that are narrow, magnetic flux may be completely expelled from a thin shell of approximately the above size after 10^5 yr. This shell may insulate lower conductivity outer layers, where magnetic fields can diffuse and decay faster, from fields maintained in the highly conducting deep core.

Read this paper on arXiv…

W. Ho, N. Andersson and V. Graber
Mon, 27 Nov 2017
5/78

Comments: 6 pages, 5 figures; accepted for publication in Physical Review C

Toward electrodynamics of unconventional phases of dilute nuclear matter [CL]

Posted on by

http://arxiv.org/abs/1711.06984


The phase diagram of isospin-asymmetrical nuclear matter may feature a number of unconventional phases, which include the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate, the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase, and the heterogeneous phase-separated phase. Because the Cooper pairs of the condensate carry a single unit of charge, these phases are charged superconductors and respond to electromagnetic gauge fields by either forming domains (type-I superconductivity) or quantum vortices (type-II superconductivity). We evaluate the Ginzburg-Landau (GL) parameter across the phase diagram and find that the unconventional phases of isospin-asymmetrical nuclear matter are good type-II superconductors and should form Abrikosov vortices with twice the quantum of magnetic flux. We also find that the LOFF phase at the boundary of the transition to the type-I state, with the GL parameter being close to the critical value $1/\sqrt{2}$.

Read this paper on arXiv…

A. Sedrakian and J. Clark
Tue, 21 Nov 17
75/79

Comments: Invited contribution presented by A. S. at the 19th International Conference on Recent Progress in Many-Body Theories, June 25-30, 2017, APCTP, Pohang, Korea, v1: 8 pages, 2 figs

Three-nucleon forces and superfluidity in neutron matter [CL]

Posted on by

http://arxiv.org/abs/1705.10463


The existence of superfluidity of the neutron component in the core of a neutron star, associated specifically with triplet $P-$wave pairing, is currently an open question that is central to interpretation of the observed cooling curves and other neutron-star observables. Ab initio theoretical calculations aimed at resolving this issue face unique challenges in the relevant high-density domain, which reaches beyond the saturation density of symmetrical nuclear matter. These issues include uncertainties in the three-nucleon (3N) interaction and in the effects of strong short-range correlations — and more generally of in-medium modification of nucleonic self-energies and interactions. A survey of existing solutions to the gap equations in the triplet channel shows that the separate or combined impacts of 3N forces, coupled channels, and mass renormalization range from moderate to strong to devastating, thus motivating a detailed analysis of the competing effects. In the present work we track the effects of the 3N force and in-medium modifications in the representative case of the $^3P_2$ channel, based on the Argonne V18 two-nucleon (2N) interaction supplemented by 3N interactions of the Urbana IX family. Sensitivity of the results to the input interaction is clearly demonstrated, while consistency issues arise with respect to the simultaneous treatment of 3N forces and in-medium effects. We consider this pilot study as the first step towards a systematic and comprehensive exploration of coupled-channel $^3P F_2$ pairing using a broad range of 2N and 3N interactions from the current generation of refined semi-phenomenological models and models derived from chiral effective field theory.

Read this paper on arXiv…

P. Papakonstantinou and J. Clark
Wed, 31 May 17
-196/48

Comments: 17 pages, incl. 6 figures; intended for a special issue of the Journal of Low Temperature Physics on superfluidity and pairing phenomena

Composition of nuclear matter with light clusters and Bose-Einstein condensation of $α$ particles [CL]

Posted on by

http://arxiv.org/abs/1705.02525


The Bose-Einstein condensation of $\alpha$ partciles in the multicomponent environment of dilute, warm nuclear matter is studied. We consider the cases of matter composed of light clusters with mass numbers $A\leq 4$ and matter that in addition these clusters contains $\isotope[56]{Fe}$ nuclei. We apply the quasiparticle gas model which treats clusters as bound states with infinite life-time and binding energies independent of temperature and density. We show that the $\alpha$ particles can form a condensate at low temperature $T\le 2$ MeV in such matter in the first case. When the $\isotope[56]{Fe}$ nucleus is added to the composition the cluster abundances are strongly modified at low temperatures, with an important implication that the $\alpha$ condensation at these temperatures is suppressed.

Read this paper on arXiv…

X. Wu, S. Wang, A. Sedrakian, et. al.
Tue, 9 May 17
75/82

Comments: 15 pages, 8 figures

Critical magnetic fields in a superconductor coupled to a superfluid [CL]

Posted on by

http://arxiv.org/abs/1704.01575


We study a superconductor that is coupled to a superfluid via density and derivative couplings. Starting from a Lagrangian for two complex scalar fields, we derive a temperature-dependent Ginzburg-Landau potential, which is then used to compute the phase diagram at nonzero temperature and external magnetic field. This includes the calculation of the critical magnetic fields for the transition to an array of magnetic flux tubes, based on an approximation for the interaction between the flux tubes. We find that the transition region between type-I and type-II superconductivity changes qualitatively due to the presence of the superfluid: the phase transitions at the upper and lower critical fields in the type-II regime become first order, opening the possibility of clustered flux tube phases. These flux tubes clusters may be realized in the core of neutron stars, where superconducting protons are expected to be coupled to superfluid neutrons.

Read this paper on arXiv…

A. Haber and A. Schmitt
Fri, 7 Apr 17
6/50

Comments: 27 pages, 7 figures

High quality factor manganese-doped aluminum lumped-element kinetic inductance detectors sensitive to frequencies below 100 GHz [IMA]

Posted on by

http://arxiv.org/abs/1701.08461


Aluminum lumped-element kinetic inductance detectors (LEKIDs) sensitive to millimeter-wave photons have been shown to exhibit high quality factors, making them highly sensitive and multiplexable. The superconducting gap of aluminum limits aluminum LEKIDs to photon frequencies above 100 GHz. Manganese-doped aluminum (Al-Mn) has a tunable critical temperature and could therefore be an attractive material for LEKIDs sensitive to frequencies below 100 GHz if the internal quality factor remains sufficiently high when manganese is added to the film. To investigate, we measured some of the key properties of Al-Mn LEKIDs. A prototype eight-element LEKID array was fabricated using a 40 nm thick film of Al-Mn deposited on a 500 {\mu}m thick high-resistivity, float-zone silicon substrate. The manganese content was 900 ppm, the measured $T_c = 694\pm1$ mK, and the resonance frequencies were near 150 MHz. Using measurements of the forward scattering parameter $S_{21}$ at various bath temperatures between 65 and 250 mK, we determined that the Al-Mn LEKIDs we fabricated have internal quality factors greater than $2 \times 10^5$, which is high enough for millimeter-wave astrophysical observations. In the dark conditions under which these devices were measured, the fractional frequency noise spectrum shows a shallow slope that depends on bath temperature and probe tone amplitude, which could be two-level system noise. The anticipated white photon noise should dominate this level of low-frequency noise when the detectors are illuminated with millimeter-waves in future measurements. The LEKIDs responded to light pulses from a 1550 nm light-emitting diode, and we used these light pulses to determine that the quasiparticle lifetime is 60 {\mu}s.

Read this paper on arXiv…

G. Jones, B. Johnson, M. Abitbol, et. al.
Tue, 31 Jan 17
11/58

Comments: 5 pages, 4 figures

Vortex buoyancy in superfluid and superconducting neutron stars [HEAP]

Posted on by

http://arxiv.org/abs/1701.06870


Buoyancy of proton vortices is considered as one of the important mechanisms of magnetic field expulsion from the superconducting interiors of neutron stars. Here we show that the generally accepted expression for the buoyancy force is not correct and should be modified. The correct expression is derived for both neutron and proton vortices. It is argued that this force is already contained in the coarse-grained hydrodynamics of Bekarevich & Khalatnikov and its various multifluid extensions, but is absent in the hydrodynamics of Hall. Some potentially interesting buoyancy-related effects are briefly discussed.

Read this paper on arXiv…

V. Dommes and M. Gusakov
Wed, 25 Jan 17
18/74

Comments: 6 pages, accepted for publication in MNRAS Letters

Microscopic Study of ${}^1{S_0}$ Superfluidity in Dilute Neutron Matter [CL]

Posted on by

http://arxiv.org/abs/1612.02188


Singlet $S$-wave superfluidity of dilute neutron matter is studied within the correlated BCS method, which takes into account both pairing and short-range correlations. First, the equation of state (EOS) of normal neutron matter is calculated within the Correlated Basis Function (CBF) method in lowest cluster order using the ${}^1{S_0}$ and ${}^3P$ components of the Argonne $V_{18}$ potential, assuming trial Jastrow-type correlation functions. The ${}^1{S_0}$ superfluid gap is then calculated with the corresponding component of the Argonne $V_{18}$ potential and the optimally determined correlation functions. The dependence of our results on the chosen forms for the correlation functions is studied, and the role of the $P$-wave channel is investigated. Where comparison is meaningful, the values obtained for the ${}^1{S_0}$ gap within this simplified scheme are consistent with the results of similar and more elaborate microscopic methods.

Read this paper on arXiv…

G. Pavlou, E. Mavrommatis, C. Moustakidis, et. al.
Thu, 8 Dec 16
35/69

Comments: 9 pages, 6 figures

Nonequilibrium interpretation of DC properties of NbN superconducting hot electron bolometers [CL]

Posted on by

http://arxiv.org/abs/1609.06116


We present a physically consistent interpretation of the dc electrical properties of niobiumnitride (NbN)-based superconducting hot-electron bolometer (HEB-) mixers, using concepts of nonequilibrium superconductivity. Through this we clarify what physical information can be extracted from the resistive transition and the dc current-voltage characteristics, measured at suitably chosen temperatures, and relevant for device characterization and optimization. We point out that the intrinsic spatial variation of the electronic properties of disordered superconductors, such as NbN, leads to a variation from device to device.

Read this paper on arXiv…

M. Shcherbatenko, I. Tretyakov, Y. Lobanov, et. al.
Fri, 7 Oct 16
14/75

Comments: N/A

Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors [IMA]

Posted on by

http://arxiv.org/abs/1609.06352


We present a technique for increasing the internal quality factor of kinetic inductance detectors (KIDs) by nulling ambient magnetic fields with a properly applied magnetic field. The KIDs used in this study are made from thin-film aluminum, they are mounted inside a light-tight package made from bulk aluminum, and they are operated near $150 \, \mathrm{mK}$. Since the thin-film aluminum has a slightly elevated critical temperature ($T_\mathrm{c} = 1.4 \, \mathrm{K}$), it therefore transitions before the package ($T_\mathrm{c} = 1.2 \, \mathrm{K}$), which also serves as a magnetic shield. On cooldown, ambient magnetic fields as small as approximately $30 \, \mathrm{\mu T}$ can produce vortices in the thin-film aluminum as it transitions because the bulk aluminum package has not yet transitioned and therefore is not yet shielding. These vortices become trapped inside the aluminum package below $1.2 \, \mathrm{K}$ and ultimately produce low internal quality factors in the thin-film superconducting resonators. We show that by controlling the strength of the magnetic field present when the thin film transitions, we can control the internal quality factor of the resonators. We also compare the noise performance with and without vortices present, and find no evidence for excess noise beyond the increase in amplifier noise, which is expected with increasing loss.

Read this paper on arXiv…

D. Flanigan, B. Johnson, M. Abitbol, et. al.
Thu, 22 Sep 16
13/62

Comments: 5 pages, 4 figures

Microscopic Calculations of Vortex-Nucleus Interaction in the Neutron Star Crust [CL]

Posted on by

http://arxiv.org/abs/1609.03865


We investigate the dynamics of a quantized vortex and a nuclear impurity immersed in a neutron superfluid within a fully microscopic time-dependent three-dimensional approach. The magnitude and even the sign of the force between the quantized vortex and the nuclear impurity have been a matter of debate for over four decades. We determine that the vortex and the impurity repel at neutron densities, 0.014 fm$^{-3}$ and 0.031 fm$^{-3}$, which are relevant to the neutron star crust and the origin of glitches, while previous calculations have concluded that the force changes its sign between these two densities and predicted contradictory signs. The magnitude of the force increases with the density of neutron superfluid, while the magnitude of the pairing gap decreases in this density range.

Read this paper on arXiv…

K. Sekizawa, G. Wlazlowski, P. Magierski, et. al.
Wed, 14 Sep 16
58/75

Comments: 4 pages, 2 figures, Talk given at the 14th International Symposium on “Nuclei in the Cosmos” (NIC-XIV), June 19-24, 2016, Toki Messe, Niigata, Japan

Superconducting NbTiN Thin Films with Highly Uniform Properties over a 100 mm diameter Wafer [IMA]

Posted on by

http://arxiv.org/abs/1609.01526


Uniformity in thickness and electronic properties of superconducting niobium titanium nitride (NbTiN) thin films is a critical issue for upscaling superconducting electronics, such as microwave kinetic inductance detectors for submillimeter wave astronomy. In this article we make an experimental comparison between the uniformity of NbTiN thin films produced by two DC magnetron sputtering systems with vastly different target sizes: the Nordiko 2000 equipped with a circular 100mm diameter target, and the Evatec LLS801 with a rectangular target of 127 mm x 444.5 mm. In addition to the films deposited staticly in both systems, we have also deposited films in the LLS801 while shuttling the substrate in front of the target, with the aim of further enhancing the uniformity. Among these three setups, the LLS801 system with substrate shuttling has yielded the highest uniformity in film thickness (+/-2%), effective resistivity (decreasing by 5% from center to edge), and superconducting critical temperature (T_c = 15.0 K – 15.3 K) over a 100 mm diameter wafer. However, the shuttling appears to increase the resistivity by almost a factor of 2 compared to static deposition. Surface SEM inspections suggest that the shuttling could have induced a different mode of microstructural film growth.

Read this paper on arXiv…

D. Thoen, B. Bos, E. Haalebos, et. al.
Wed, 7 Sep 16
47/61

Comments: IEEE Transactions on Applied Superconductivity, Applied Superconductor Conference 2016, 5 pages, 3 figures

Reactive magnetron sputter deposition of superconducting niobium titanium nitride thin films with different target sizes [CL]

Posted on by

http://arxiv.org/abs/1609.01265


The superconducting critical temperature (Tc>15 K) of niobium titanium nitride (NbTiN) thin films allows for low-loss circuits up to 1.1 THz, enabling on-chip spectroscopy and multi-pixel imaging with advanced detectors. The drive for large scale detector microchips is demanding NbTiN films with uniform properties over an increasingly larger area. This article provides an experimental comparison between two reactive d.c. sputter systems with different target sizes: a small target (100 mm diameter) system and a large target (127 mm x 444.5 mm) one, with the aim of improving the film uniformity using the large target system. We focus on the Tc of the films and I-V characteristics of the sputter plasma, and we find that both systems are capable of depositing films with Tc>15 K. We find that these films are deposited within the transition from metallic to compound sputtering, at the point where target nitridation most strongly depends on nitrogen flow. Key in the deposition optimization is to increase the system’s pumping speed and gas flows to counteract the hysteretic effects induced by the target size. Using the I-V characteristics as a guide proves to be an effective way to optimize a reactive sputter system, for it can show whether the optimal deposition regime is hysteresis-free and accessible.

Read this paper on arXiv…

B. Bos, D. Thoen, E. Haalebos, et. al.
Tue, 6 Sep 16
66/74

Comments: Presented at Applied Superconductivity Conference 2016. Consists of 5 pages and 4 figures

Surprises with Nonrelativistic Naturalness [CL]

Posted on by

http://arxiv.org/abs/1608.06287


We explore the landscape of technical naturalness for nonrelativistic systems, finding surprises which challenge and enrich our relativistic intuition already in the simplest case of a single scalar field. While the immediate applications are expected in condensed matter and perhaps in cosmology, the study is motivated by the leading puzzles of fundamental physics involving gravity: The cosmological constant problem and the Higgs mass hierarchy problem.

Read this paper on arXiv…

P. Horava
Wed, 24 Aug 16
43/52

Comments: 15 pages, a few figures

$^3P_2$ Superfluids Are Topological [CL]

Posted on by

http://arxiv.org/abs/1607.07266


We clarify the topology of the $^3P_2$ superfluidity which is expected to be realized in the cores of neutron stars and cubic odd-parity superconductors. The phase diagram includes the unitary uniaxial/biaxial nematic phases and nonunitary ferromagnetic and cyclic phases. We here show that the low-energy structures of all the phases are governed by different types of topologically protected gapless fermionic excitations: Surface Majorana fermions in nematic phases, single itinerant Majorana fermion in the ferromagnetic phase, and a quartet of itinerant Majorana fermions in the cyclic phase. Using the superfluid Fermi liquid theory, we also demonstrate that dihedral-two and -four biaxial nematic phases are thermodynamically favored in the weak coupling limit under a magnetic field. The mass acquisition of surface Majorana fermions in nematic phases is subject to symmetry.

Read this paper on arXiv…

T. Mizushima, K. Masuda and M. Nitta
Tue, 2 Aug 16
54/80

Comments: 6 pages, 3 figures + 6 pages, 2 figures (supplementary material)

Relativistic dynamics of superfluid-superconducting mixtures in the presence of topological defects and the electromagnetic field, with application to neutron stars [CL]

Posted on by

http://arxiv.org/abs/1607.01629


The relativistic dynamic equations are derived for a superfluid-superconducting mixture coupled to the electromagnetic field. For definiteness and bearing in mind possible applications of our results to neutron stars, it is assumed that the mixture is composed of superfluid neutrons, superconducting protons, and normal electrons. Proton superconductivity of both I and II types is analysed, and possible presence of neutron and proton vortices (or magnetic domains in the case of type-I proton superconductivity) is allowed for. The derived equations neglect all dissipative effects except for the mutual friction dissipation and are valid for arbitrary temperatures (i.e. they do not imply that all nucleons are paired), which is especially important for magnetar conditions. It is demonstrated that these general equations can be substantially simplified for typical neutron stars, for which a kind of magnetohydrodynamic approximation is justified. Our results are compared to the nonrelativistic formulations existing in the literature and a discrepancy is found. Namely, it is shown that, generally, the electric displacement ${\pmb D}$ does not coincide with the electric field ${\pmb E}$, contrary to what is stated in the previous works. The relativistic framework developed here is easily extendable to account for more sophisticated microphysics models and it provides the necessary basis for realistic modelling of neutron stars.

Read this paper on arXiv…

M. Gusakov and V. Dommes
Thu, 7 Jul 16
22/43

Comments: 39 pages, submitted to PRD, comments welcome

AC bias characterization of low noise bolometers for SAFARI using an Open-Loop Frequency Domain SQUID-based multiplexer operating between 1 and 5 MHz [CL]

Posted on by

http://arxiv.org/abs/1604.02593


SRON is developing the Frequency Domain Multiplexing (FDM) readout and the ultra low NEP TES bolometers array for the infrared spectrometer SAFARI on board of the Japanese space mission SPICA. The FDM prototype of the instrument requires critical and complex optimizations. For single pixel characterization under AC bias we are developing a simple FDM system working in the frequency range from 1 to 5 MHz, based on the open loop read-out of a linearized two-stage SQUID amplifier and high Q lithographic LC resonators. We describe the details of the experimental set-up required to achieve low power loading (< 1 fW) and low noise (NEP $\sim 10^{-19} W/Hz^{1/2}$) in the TES bolometers. We conclude the paper by comparing the performance of a $4 \cdot 10^{-19} W/Hz^{1/2}$ TES bolometer measured under DC and AC bias.

Read this paper on arXiv…

L. Gottardi, M. Bruijn, J. Gao, et. al.
Tue, 12 Apr 16
20/63

Comments: 6 pages, 5 figures

Development of TES-based detectors array for the X-ray Integral Field Unit (X-IFU) on the future x-ray observatory ATHENA [IMA]

Posted on by

http://arxiv.org/abs/1604.00553


We are developing transition-edge sensor (TES)-based microcalorimeters for the X-ray Integral Field Unit (XIFU) of the future European X-Ray Observatory Athena. The microcalorimeters are based on TiAu TESs coupled to 250{\mu}m squared, AuBi absorbers. We designed and fabricated devices with different contact geometries between the absorber and the TES to optimise the detector performance and with different wiring topology to mitigate the self-magnetic field. The design is tailored to optimise the performance under Frequency Domain Multiplexing. In this paper we review the main design feature of the pixels array and we report on the performance of the 18 channels, 2-5MHz frequency domain multiplexer that will be used to characterised the detector array.

Read this paper on arXiv…

L. Gottardi, H. Akamatsu, D. Barret, et. al.
Tue, 5 Apr 16
28/67

Comments: 9 pages, 8 figures

Development of the superconducting detectors and read-out for the X-IFU instrument on board of the X-ray observatory Athena [IMA]

Posted on by

http://arxiv.org/abs/1604.00670


The Advanced Telescope for High-Energy Astrophysics (Athena) has been selected by ESA as its second large-class mission. The future European X-ray observatory will study the hot and energetic Universe with its launch foreseen in 2028. Microcalorimeters based on superconducting Transition-edge sensor (TES) are the chosen technology for the detectors array of the X-ray Integral Field Unit (X-IFU) on board of Athena. The X-IFU is a 2-D imaging integral-field spectrometer operating in the soft X-ray band (0.3 -12 keV). The detector consists of an array of 3840 TESs coupled to X-ray absorbers and read out in the MHz bandwidth using Frequency Domain Multiplexing (FDM) based on Superconducting QUantum Interference Devices (SQUIDs). The proposed design calls for devices with a high filling-factor, high quantum e?ciency, relatively high count-rate capability and an energy resolution of 2.5 eV at 5.9 keV. The paper will review the basic principle and the physics of the TES-based microcalorimeters and present the state-of-the art of the FDM read-out.

Read this paper on arXiv…

L. Gottardi, H. Akamatsu, M. Bruijn, et. al.
Tue, 5 Apr 16
44/67

Comments: 4 pages,4 figures, available on line (this http URL)

Weak-Link Phenomena in AC-Biased Transition Edge Sensors [CL]

Posted on by

http://arxiv.org/abs/1604.00680


It has been recently demonstrated that superconducting transition edge sensors (TESs) behave as weak-links due to longitudinally induced superconductivity from the leads with higher Tc. In this work we study the implication of this behaviour for TES-based bolometers and microcalorimeter under ac bias. The TESs are read-out at frequencies between 1 and 5 MHz by a Frequency Domain Multiplexer based on a linearised two-stage SQUID amplifier and high- Q lithographically made superconducting LC resonators. In particular, we focus on SRON TiAu TES bolometers with a measured dark Noise Equivalent Power (NEP) of $3.2 \cdot 10^{-19} W/Hz^{1/2}$ developed for the short wavelength band for the instrument SAFARI on the SPICA telescope.

Read this paper on arXiv…

L. Gottardi, H. Akamatsu, M. Bruijn, et. al.
Tue, 5 Apr 16
66/67

Comments: 6 pages, 5 figure

Relativistic formulation of the Hall-Vinen-Bekarevich-Khalatnikov superfluid hydrodynamics [CL]

Posted on by

http://arxiv.org/abs/1601.07732


The relativistic analogue of the Hall-Vinen-Bekarevich-Khalatnikov (HVBK) hydrodynamics is derived making use of the phenomenological method similar to that used by Bekarevich and Khalatnikov [1] in their derivation of HVBK-hydrodynamics. The resulting equations describe a finite-temperature superfluid liquid with the distributed vorticity. The main dissipative effects, including mutual friction, are taken into account. The proposed hydrodynamics is needed for reliable modeling of the dynamical properties of superfluid neutron stars.

Read this paper on arXiv…

M. Gusakov
Wed, 3 Feb 16
3/54

Comments: 23 pages, submitted to PRD on 16 October, 2015

Development of Lumped Element Kinetic Inductance Detectors for the W-Band [IMA]

Posted on by

http://arxiv.org/abs/1601.01466


We are developing a Lumped Element Kinetic Inductance Detector (LEKID) array able to operate in the W-band (75-110 GHz) in order to perform ground-based Cosmic Microwave Background (CMB) and mm-wave astronomical observations. The W-band is close to optimal in terms of contamination of the CMB from Galactic synchrotron, free-free, and thermal interstellar dust. In this band, the atmosphere has very good transparency, allowing interesting ground-based observations with large (>30 m) telescopes, achieving high angular resolution (<0.4 arcmin). In this work we describe the startup measurements devoted to the optimization of a W-band camera/spectrometer prototype for large aperture telescopes like the 64 m SRT (Sardinia Radio Telescope). In the process of selecting the best superconducting film for the LEKID, we characterized a 40 nm thick Aluminum 2-pixel array. We measured the minimum frequency able to break CPs (i.e. $h\nu=2\Delta\left(T_{c}\right)=3.5k_{B}T_{c}$) obtaining $\nu=95.5$ GHz, that corresponds to a critical temperature of 1.31 K. This is not suitable to cover the entire W-band. For an 80 nm layer the minimum frequency decreases to 93.2 GHz, which corresponds to a critical temperature of 1.28 K; this value is still suboptimal for W-band operation. Further increase of the Al film thickness results in bad performance of the detector. We have thus considered a Titanium-Aluminum bi-layer (10 nm thick Ti + 25 nm thick Al, already tested in other laboratories), for which we measured a critical temperature of 820 mK and a cut-on frequency of 65 GHz: so this solution allows operation in the entire W-band.

Read this paper on arXiv…

A. Paiella, A. Coppolecchia, M. Castellano, et. al.
Fri, 8 Jan 16
35/51

Comments: 16th International Workshop on Low Temperature Detectors, Grenoble 20-24 July 2015, Journal of Low Temperature Physics, Accepted

Reproducing sterile neutrinos and the behavior of flavor oscillations with superconducting-magnetic proximity effects [CL]

Posted on by

http://arxiv.org/abs/1601.00913


The physics of a superconductor subjected to a magnetic field is known to be equivalent to neutrino oscillations. Examining the properties of singlet-triplet oscillations in the magnetic field, a sterile neutrino–shown to be a Majorana fermion–is suggested to be represented by singlet Cooper pairs and moderates flavor oscillations between three flavor neutrinos (triplet Cooper pairs). A superconductor-exchange spring system’s rotating magnetization profile is used to simulate the mass-flavor oscillations in the neutrino case and the physics of neutrino oscillations are discussed. Symmetry protected triplet components are presented as weak process states. Phases acquired due to the Fulde-Ferrell-Larkin-Ovchinnikov effect produce a complex phase that may be responsible for charge-parity violation in flavor oscillations.

Read this paper on arXiv…

T. Baker
Wed, 6 Jan 16
31/43

Comments: 14 pages, 6 figures

Photon noise from chaotic and coherent millimeter-wave sources measured with horn-coupled, aluminum lumped-element kinetic inductance detectors [IMA]

Posted on by

http://arxiv.org/abs/1510.06609


We report photon-noise limited performance of horn-coupled, aluminum lumped-element kinetic inductance detectors at millimeter wavelengths. The detectors are illuminated by a millimeter-wave source that uses an active multiplier chain to produce radiation between 140 and 160 GHz. We feed the multiplier with either amplified broadband noise or a continuous-wave tone from a microwave signal generator. We demonstrate that the detector response over a 40 dB range of source power is well-described by a simple model that considers the number of quasiparticles. The detector noise-equivalent power (NEP) is dominated by photon noise when the absorbed power is greater than approximately 1 pW, which corresponds to $\mathrm{NEP} \approx 2 \times 10^{-17} \; \mathrm{W} \; \mathrm{Hz}^{-1/2}$, referenced to absorbed power. At higher source power levels we observe the relationships between noise and power expected from the photon statistics of the source signal: $\mathrm{NEP} \propto P$ for broadband (chaotic) illumination and $\mathrm{NEP} \propto P^{1/2}$ for continuous-wave (coherent) illumination. We develop a detailed model for the device noise and demonstrate absolute calibration of the absorbed power in both source modes using the scaling of the photon noise with power.

Read this paper on arXiv…

D. Flanigan, H. McCarrick, G. Jones, et. al.
Fri, 23 Oct 15
52/63

Comments: 5 pages, 2 figures; includes supplemental material

Cascading Multicriticality in Nonrelativistic Spontaneous Symmetry Breaking [CL]

Posted on by

http://arxiv.org/abs/1507.06992


Without Lorentz invariance, spontaneous global symmetry breaking can lead to multicritical Nambu-Goldstone modes with a higher-order low-energy dispersion $\omega\sim k^n$ ($n=2,3,\ldots$), whose naturalness is protected by polynomial shift symmetries. Here we investigate the role of infrared divergences and the nonrelativistic generalization of the Coleman-Hohenberg-Mermin-Wagner (CHMW) theorem. We find novel cascading phenomena with large hierarchies between the scales at which the value of $n$ changes, leading to an evasion of the “no-go” consequences of the relativistic CHMW theorem.

Read this paper on arXiv…

T. Griffin, K. Grosvenor, P. Horava, et. al.
Tue, 28 Jul 15
21/70

Comments: 5 pages, 1 figure

Highly Multiplexible Thermal Kinetic Inductance Detectors for X-Ray Imaging Spectroscopy [IMA]

Posted on by

http://arxiv.org/abs/1506.07537


For X-ray imaging spectroscopy, high spatial resolution over a large field of view is often as important as high energy resolution, but current X-ray detectors do not provide both in the same device. Thermal Kinetic Inductance Detectors (TKIDs) are being developed as they offer a feasible way to combine the energy resolution of transition edge sensors with pixel counts approaching CCDs and thus promise significant improvements for many X-ray spectroscopy applications. TKIDs are a variation of Microwave Kinetic Inductance Detectors (MKIDs) and share their multiplexibility: working MKID arrays with 2024 pixels have recently been demonstrated and much bigger arrays are under development. In this work, we present our first working TKID prototypes which are able to achieve an energy resolution of 75 eV at 5.9 keV, even though their general design still has to be optimized. We further describe TKID fabrication, characterization, multiplexing and working principle and demonstrate the necessity of a data fitting algorithm in order to extract photon energies. With further design optimizations we expect to be able to improve our TKID energy resolution to less than 10 eV at 5.9 keV.

Read this paper on arXiv…

G. Ulbricht, B. Mazin, P. Szypryt, et. al.
Fri, 26 Jun 15
10/44

Comments: 7 pages, 4 figures, accepted for publication in Applied Physics Letters

The non-equilibrium response of a superconductor to pair-breaking radiation measured over a broad frequency band [CL]

Posted on by

http://arxiv.org/abs/1505.06191


We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice this is the first measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.

Read this paper on arXiv…

P. Visser, S. Yates, T. Guruswamy, et. al.
Mon, 25 May 15
42/47

Comments: N/A

Multiple Period States of the Superfluid Fermi Gas in an Optical Lattice [CL]

Posted on by

http://arxiv.org/abs/1503.07976


We study multiple period states of a superfluid Fermi gas in an optical lattice along the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover. The existence of states whose period is a multiple of the lattice spacing is a consequence of the non-linear behavior of the gas, which is due to the presence of the order parameter associated with superfluidity. By solving Bogoliubov-de Gennes equations we find that, in the BCS side of the crossover, the multiple period states can be energetically favorable compared to the normal Bloch states and their survival time against dynamical instability drastically increases, suggesting that these states can be accessible in current experiments with ultracold gases. This is in sharp contrast to the situation in BECs.

Read this paper on arXiv…

S. Yoon, F. Dalfovo, T. Nakatsukasa, et. al.
Mon, 30 Mar 15
40/65

Comments: 5 pages, 5 figures

Heat transfer coefficient saturation in superconducting Nb tunnel junctions contacted to a NbTiN circuit and an Au energy relaxation layer [CL]

Posted on by

http://arxiv.org/abs/1412.3388


In this paper we present the experimental realization of a Nb tunnel junction connected to a high-gap superconducting NbTiN embedding circuit. We investigate relaxation of nonequilibrium quasiparticles in a small volume Au layer between the Nb tunnel junction and the NbTiN circuit. We find a saturation in the effective heat-transfer coefficient consistent with a simple theoretical model. This saturation is determined by the thickness of the Au layer. Our findings are important for the design of the ideal Au energy relaxation layer for practical SIS heterodyne mixers and we suggest two geometries, one, using a circular Au layer and, two, using a half-circular Au layer. Our work is concluded with an outlook of our future experiments.

Read this paper on arXiv…

S. Selig, M. Westig, K. Jacobs, et. al.
Thu, 11 Dec 14
26/48

Comments: Applied Superconductivity Conference 2014

Some comments on a new type of superconducting gravity wave detector [IMA]

Posted on by

http://arxiv.org/abs/1409.6362


We have recently suggested a new approach and design of an ultra-sensitive gravity wave detector antenna based on superconductivity. The idea was described in a short paper [1]: this http URL, in entries on the arXiv [2]: arXiv:1111.2655, and at various conferences. Here we would like to explain in a more detailed manner the motivation for and the advantages of our approach.

Read this paper on arXiv…

A. Guliana, J. Foremanb, V. Nikoghosyana, et. al.
Wed, 24 Sep 14
37/62

Comments: N/A

Performance of Hybrid NbTiN-Al Microwave Kinetic Inductance Detectors as Direct Detectors for Sub-millimeter Astronomy [IMA]

Posted on by

http://arxiv.org/abs/1408.3314


In the next decades millimeter and sub-mm astronomy requires large format imaging arrays and broad-band spectrometers to complement the high spatial and spectral resolution of the Atacama Large Millimeter/sub-millimeter Array. The desired sensors for these instruments should have a background limited sensitivity and a high optical efficiency and enable arrays thousands of pixels in size. Hybrid microwave kinetic inductance detectors consisting of NbTiN and Al have shown to satisfy these requirements. We present the second generation hybrid NbTiN-Al MKIDs, which are photon noise limited in both phase and amplitude readout for loading levels $P_{850GHz} \geq 10$ fW. Thanks to the increased responsivity, the photon noise level achieved in phase allows us to simultaneously read out approximately 8000 pixels using state-of-the-art electronics. In addition, the choice of superconducting materials and the use of a Si lens in combination with a planar antenna gives these resonators the flexibility to operate within the frequency range $0.09 < \nu < 1.1$ THz. Given these specifications, hybrid NbTiN-Al MKIDs will enable astronomically usable kilopixel arrays for sub-mm imaging and moderate resolution spectroscopy.

Read this paper on arXiv…

R. Janssen, J. Baselmans, A. Endo, et. al.
Fri, 15 Aug 14
8/45

Comments: 7 pages, 3 figures. Presented at SPIE Astronomical Telescopes and Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII

Photon-noise limited sensitivity in titanium nitride kinetic inductance detectors [IMA]

Posted on by

http://arxiv.org/abs/1406.4010


We demonstrate photon-noise limited performance at sub-millimeter wavelengths in feedhorn-coupled, microwave kinetic inductance detectors (MKIDs) made of a TiN/Ti/TiN trilayer superconducting film, tuned to have a transition temperature of 1.4 K. The lumped-element detector design enables dual-polarization sensitivity. The devices are fabricated on a silicon-on-insulator (SOI) wafer. Micro-machining of the SOI wafer backside creates a quarter-wavelength backshort optimized for efficient coupling at 250 $\mu$m. Using frequency read out and when viewing a variable temperature thermal source, we measure device noise consistent with photon noise when the incident optical power is $>$1 pW, corresponding to noise equivalent powers $>$ 4$\times 10^{-17}$ W/$\sqrt{\mathrm{Hz}}$. This sensitivity makes these devices suitable for broadband photometric applications at these wavelengths.

Read this paper on arXiv…

J. Hubmayr, J. Beall, D. Becker, et. al.
Tue, 17 Jun 14
10/63

Comments: submitted to APL

RF heating efficiency of terahertz superconducting hot-electron bolometer [CL]

Posted on by

http://arxiv.org/abs/1404.5276


The system of differential equations for heat balance in a superconducting HEB and for the HEB electrical circuit is written in recurrent form and solved numerically by the Euler method. Dependence of the HEB resistance on the transport current is taken into account. RF heating efficiency, absorbed local oscillator (LO) power and conversion gain of the HEB mixer are calculated. It is shown that calculated conversion gain is in excellent agreement with experiment. It is shown that substitution of calculated RF heating efficiency and absorbed LO power to expressions for conversion gain and noise temperature given by the analytical small signal model of HEB yields excellent agreement with corresponding measured values.

Read this paper on arXiv…

S. Maslennikov
Tue, 22 Apr 14
38/54

Axion mass estimates from resonant Josephson junctions [CL]

Posted on by

http://arxiv.org/abs/1403.5676


Recently it has been proposed that dark matter axions from the galactic halo can produce a small Shapiro step-like signal in Josephson junctions whose Josephson frequency resonates with the axion mass [C. Beck, PRL 111, 231801 (2013)]. Here we show that the axion field equations in a voltage-driven Josephson junction environment allow for a nontrivial solution where the axion-induced electric current manifests itself as an oscillating supercurrent. The linear change of phase associated with this nontrivial solution implies the existence of a large magnetic field in a tiny surface area of the weak link region of the junction which makes incoming axions decay into microwave photons. We derive a condition for the design of Josephson junction experiments so that they can act as optimum axion detectors. Four independent recent experiments are discussed in this context. The observed Shapiro step anomalies of all four experiments consistently point towards an axion mass of $(110 \pm 2)\mu $eV. This mass value is compatible with the recent BICEP2 results and implies that Peccei-Quinn symmetry breaking was taking place after inflation.

Read this paper on arXiv…

C. Beck
Tue, 25 Mar 14
40/79

Electron-Phonon Coupling on the NbSi Transition Edge Sensors [IMA]

Posted on by

http://arxiv.org/abs/1402.3672


We have built an electron-phonon coupling model to describe the behavior of the NbxSi1-x transition edge sensor (TES) bolometers, fabricated by electron-beam coevaporation and photolithography techniques on a 2-inch silicon wafer. The resistance versus temperature curves of several sensors with different thickness are measured with different bias currents, ranging from 200 nA to 10 micro A, and the electron-phonon coupling coefficient and the electron-phonon thermal conductance are calculated herein. Our values are quite comparable with those in metallic TES samples of other groups using different measurement methods, while we are using the transition region of our TES sample to calculate the electron-phonon coupling interaction.

Read this paper on arXiv…

S. Liu, S. Marnieros, L. Dumoulin, et. al.
Tue, 18 Feb 14
17/72

High optical efficiency and photon noise limited sensitivity of microwave kinetic inductance detectors using phase readout [CL]

Posted on by

http://arxiv.org/abs/1311.2429


We demonstrate photon noise limited performance in both phase and amplitude readout in microwave kinetic inductance detectors (MKIDs) consisting of NbTiN and Al, down to 100 fW of optical power. We simulate the far field beam pattern of the lens-antenna system used to couple radiation into the MKID and derive an aperture efficiency of 75%. This is close to the theoretical maximum of 80% for a single-moded detector. The beam patterns are verified by a detailed analysis of the optical coupling within our measurement setup.

Read this paper on arXiv…

Tue, 12 Nov 13
2/63