Observational constraints on quantum decoherence during inflation [CEA]

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

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

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

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

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

M. Hippke
Mon, 22 Jan 2018
39/52

Comments: 3 pages, 1 figure

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

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

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

Comments: 68 pages, 26 figures, 9 tables

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

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

M. Hippke
Mon, 18 Dec 17
29/49

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

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Does light from steady sources bear any observable imprint of the dispersive intergalactic medium? [IMA]

There has recently been some interest in the prospect of detecting ionized intergalactic baryons by examining the properties of incoherent light from background cosmological sources, namely quasars. Although the paper by \cite{lieu13} proposed a way forward, it was refuted by the later theoretical work of \cite{hir14} and observational study of \cite{hal16}. In this paper we investigated in detail the manner in which incoherent radiation passes through a dispersive medium both from the frameworks of classical and quantum electrodynamics, which led us to conclude that the premise of \cite{lieu13} would only work if the pulses involved are genuinely classical ones involving many photons per pulse, but unfortunately each photon must not be treated as a pulse that is susceptible to dispersive broadening. We are nevertheless able to change the tone of the paper at this juncture, by pointing out that because current technology allows one to measure the phase of individual modes of radio waves from a distant source, the most reliable way of obtaining irrefutable evidence of dispersion, namely via the detection of its unique signature of a quadratic spectral phase, may well be already accessible. We demonstrate how this technique is only applied to measure the column density of the ionized intergalactic medium.

R. Lieu and L. Duan
Fri, 1 Dec 17
47/68

Comments: 21 pages, 67 equations, ApJ in press

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Quantum chaos of dark matter in the Solar System [CL]

We perform time-dependent analysis of quantum dynamics of dark matter particles in the Solar System. It is shown that this problem has similarities with a microwave ionization of Rydberg atoms studied previously experimentally and analytically. On this basis it is shown that the quantum effects for chaotic dark matter dynamics become significant for dark matter mass ratio to electron mass being smaller than $2 \times 10^{-15}$. Below this border multiphoton diffusion over Rydberg states of dark matter atom becomes exponentially localized in analogy with the Anderson localization in disordered solids. The life time of dark matter in the Solar System is determined in dependence on mass ratio in the localized phase and a few photon ionization regime. Various implications of these quantum results are discussed for the capture of dark matter from Galaxy and its steady-state density distribution.

D. Shepelyansky
Thu, 23 Nov 17
48/52

Comments: 5 pages, 2 figures

Quantum chaos of dark matter in the Solar System [CL]

We perform time-dependent analysis of quantum dynamics of dark matter particles in the Solar System. It is shown that this problem has similarities with a microwave ionization of Rydberg atoms studied previously experimentally and analytically. On this basis it is shown that the quantum effects for chaotic dark matter dynamics become significant for dark matter mass ratio to electron mass being smaller than $2 \times 10^{-15}$. Below this border multiphoton diffusion over Rydberg states of dark matter atom becomes exponentially localized in analogy with the Anderson localization in disordered solids. The life time of dark matter in the Solar System is determined in dependence on mass ratio in the localized phase and a few photon ionization regime. Various implications of these quantum results are discussed for the capture of dark matter from Galaxy and its steady-state density distribution.

D. Shepelyansky
Thu, 23 Nov 17
25/52

Comments: 5 pages, 2 figures