Weekly Papers on Quantum Foundations (42)

Time-Symmetry Breaking in Hamiltonian Mechanics. II. A Memoir for Berni Julian Alder [1925-2020]. (arXiv:2010.02084v4 [physics.hist-ph] UPDATED)

2020年10月16日星期五下午8:09

physics.hist-ph updates on arXiv.org

Authors: William Graham Hoover, Carol Griswold Hoover

This memoir honors the late Berni Julian Alder, who inspired both of us with his pioneering development of molecular dynamics. Berni’s work with Tom Wainwright, described in the 1959 Scientific American[1], brought Bill to interview at Livermore in 1962. Hired by Berni, Bill enjoyed over 40 years’ research at the Laboratory. Berni, along with Edward Teller, founded UC’s Department of Applied Science in 1963. Their motivation was to attract bright students to use the laboratory’s unparalleled research facilities. In 1972 Carol was offered a joint LLNL employee-DAS student appointment at Livermore. Bill, thanks to Berni’s efforts, was already a Professor at DAS. Carol became one of Bill’s best students. Berni’s influence was directly responsible for our physics collaboration and our marriage in 1989. The present work is devoted to two early interests of Berni’s, irreversibility and shockwaves. Berni and Tom studied the irreversibility of Boltzmann’s “H function” in the early 1950s[2]. Berni called shockwaves the “most irreversible” of hydrodynamic processes[3]. Just this past summer, in simulating shockwaves with time-reversible classical mechanics, we found that reversed Runge-Kutta shockwave simulations yielded nonsteady rarefaction waves, not shocks. Intrigued by this unexpected result we studied the exponential Lyapunov instabilities in both wave types. Besides the Runge-Kutta and Leapfrog algorithms, we developed a precisely-reversible manybody algorithm based on trajectory storing, just changing the velocities’ signs to generate the reversed trajectories. Both shocks and rarefactions were precisely reversed. Separate simulations, forward and reversed, provide interesting examples of the Lyapunov-unstable symmetry-breaking models supporting the Second Law of Thermodynamics. We describe promising research directions suggested by this work.

The time distribution of quantum events. (arXiv:2010.07575v1 [quant-ph])

2020年10月16日星期五下午8:08

Danijel Jurman, Hrvoje Nikolic

quant-ph updates on arXiv.org

We develop a general theory of the time distribution of quantum events, applicable to a large class of problems such as arrival time, dwell time and tunneling time. The basic assumption is that there is a stopwatch that ticks unless an awaited event is detected, at which time the stopwatch stops. The awaited event is represented by a projection operator $\pi$, while the ideal stopwatch is modeled as a series of ideal projective measurements at different times, so that, at each of those times, the quantum state suffers an instantaneous projection with either $\bar{\pi}=1-\pi$ (when the awaited event does not happen) or $\pi$ (when the awaited event eventually happens). In the approximation in which the time $\delta t$ between the subsequent measurements is sufficiently small, we find a fairly simple general formula for the time distribution ${\cal P}(t)$, representing the probability density that the awaited event will be detected at time $t$.

Spooky Action at a Global Distance — Analysis of Space-Based Entanglement Distribution for the Quantum Internet. (arXiv:1912.06678v2 [quant-ph] UPDATED)

2020年10月16日星期五下午8:08

Sumeet Khatri, Anthony J. Brady, Renée A. Desporte, Manon P. Bart, Jonathan P. Dowling

quant-ph updates on arXiv.org

Recent experimental breakthroughs in satellite quantum communications have opened up the possibility of creating a global quantum internet using satellite links. This approach appears to be particularly viable in the near term, due to the lower attenuation of optical signals from satellite to ground, and due to the currently short coherence times of quantum memories. The latter prevents ground-based entanglement distribution using atmospheric or optical-fiber links at high rates over long distances. In this work, we propose a global-scale quantum internet consisting of a constellation of orbiting satellites that provides a continuous, on-demand entanglement distribution service to ground stations. The satellites can also function as untrusted nodes for the purpose of long-distance quantum-key distribution. We develop a technique for determining optimal satellite configurations with continuous coverage that balances both the total number of satellites and entanglement-distribution rates. Using this technique, we determine various optimal satellite configurations for a polar-orbit constellation, and we analyze the resulting satellite-to-ground loss and achievable entanglement-distribution rates for multiple ground station configurations. We also provide a comparison between these entanglement-distribution rates and the rates of ground-based quantum repeater schemes. Overall, our work provides the theoretical tools and the experimental guidance needed to make a satellite-based global quantum internet a reality.

A New Action for Cosmology. (arXiv:2010.07329v1 [gr-qc])

2020年10月16日星期五下午8:08

gr-qc updates on arXiv.org

Authors: David Sloan

We present a new action which reproduces the cosmological sector of general relativity in both the Friedmann-Lemaitre-Robertson-Walker (FLRW) and Bianchi models. This action makes no reference to the scale factor, and is of a frictional type first examined by Herglotz. We demonstrate that the extremization of this action reproduces the usual dynamics of physical observables, and the symplectification of this action is the Einstein-Hilbert action for cosmological models. We end by discussing some of the increased explanatory power produced by considering the reduced physical ontology resulting from eliminating scale.

Charge Conservation, Entropy Current, and Gravitation. (arXiv:2010.07660v1 [gr-qc])

2020年10月16日星期五下午8:08

gr-qc updates on arXiv.org

Authors: Sinya Aoki, Tetsuya Onogi, Shuichi Yokoyama

We propose a new class of vector fields to construct a conserved charge in a general field theory whose energy momentum tensor is covariantly conserved. We argue that there always exists such a vector field uniquely in a given field theory even without global symmetry and the conserved current constructed from the vector field can be identified with the entropy current of the system. As a piece of evidence we show that the conserved charge defined therefrom satisfies the first law of thermodynamics for an isotropic system with a suitable definition of temperature. We apply our formulation to several gravitational systems such as the expanding universe, Schwarzschild and BTZ black holes, and gravitational plane waves. We confirm the conservation of the proposed entropy density under any homogeneous and isotropic expansion of the universe, the precise reproduction of the Bekenstein-Hawking entropy incorporating the first law of thermodynamics, and the existence of gravitational plane wave carrying no charge, respectively.

F. J. Dyson: The Man who would make Patterns and Disturb the Universe. (arXiv:2010.07767v1 [physics.pop-ph])

2020年10月16日星期五下午8:08

gr-qc updates on arXiv.org

Authors: Patrick Das Gupta

Freeman J. Dyson, a brilliant theoretical physicist and a gifted mathematician, passed away on 28 February 2020 at the age of 96. A vignette of his outstanding contributions to physical sciences, ranging from the subject of quantum electrodynamics to gravitational waves, is provided in this article. Dyson’s futuristic ideas concerning the free will of `intelligent life’ influencing the remote future of the cosmos with `Eternal Intelligence’, Dyson tree, Dyson sphere and so on, have also been discussed briefly.

Perturbative string theory from Newtonian limit of string geometry theory. (arXiv:2002.01774v2 [hep-th] UPDATED)

2020年10月16日星期五下午8:08

gr-qc updates on arXiv.org

Authors: Matsuo Sato, Yuji Sugimoto

String geometry theory is one of the candidates of the non-perturbative formulation of string theory. In arXiv:1709.03506, the perturbative string theory is reproduced from a string geometry model coupled with a $u(1)$ gauge field on string manifolds. In this paper, we generalize this result and we show that the perturbative string theory is reproduced from any string geometry model by taking a Newtonian limit.

Entanglement and decoherence of massive particles due to gravity. (arXiv:2010.05159v2 [gr-qc] UPDATED)

2020年10月16日星期五下午8:08

gr-qc updates on arXiv.org

Authors: Daisuke Miki, Akira Matsumura, Kazuhiro Yamamoto

We analyze the dynamics of gravity-induced entanglement for N massive particles. Considering a linear configuration of these particles, we investigate the entanglement between a specific pair of particles under the influence of the gravitational interaction between the massive particles. As the particle number increases, the specific particle pair decoheres more easily due to the gravitational interaction with other particles. The time scale of the gravity-induced decoherence is found analytically. We also discuss the entanglement dynamics of initially entangled particles, which exemplify the monogamy of gravity-induced entanglement.

A stronger Bell argument for (some kind of) parameter dependence

2020年10月16日星期五下午8:08

ScienceDirect Publication: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern PhysicsScienceDirect RSShttps://www.sciencedirect.com/journal/studies-in-history-and-philosophy-of-science-part-b-studies-in-history-and-philosophy-of-modern-physicsRSS for NodeWed, 24 Jul 2019 09:46:42 GMTCopyright © 2019 Elsevier Ltd. All rights reservedImprints of the underlying structure of physical theoriesPublication date: Available online 12 July 2019Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern PhysicsAuthor(s): Jorge ManeroAbstractIn the context of scientific realism, this paper intends to provide a formal and accurate description of the structural-based ontology posited by classical mechanics, quantum mechanics and special relativity, which is preserved across the empirical domains of these theories and explain their successful predictions. Along the lines of ontic structural realism, such a description is undertaken by

Publication date: Available online 16 October 2020

Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

Author(s): Paul M. Näger

Setting Up Experimental Bell Tests with Reinforcement Learning

2020年10月16日星期五下午6:00

Alexey A. Melnikov, Pavel Sekatski, and Nicolas Sangouard

PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Alexey A. Melnikov, Pavel Sekatski, and Nicolas Sangouard

Finding optical setups producing measurement results with a targeted probability distribution is hard, as a priori the number of possible experimental implementations grows exponentially with the number of modes and the number of devices. To tackle this complexity, we introduce a method combining re…

[Phys. Rev. Lett. 125, 160401] Published Fri Oct 16, 2020

Believing the Unbelievable

2020年10月15日星期四上午2:05