Weekly Papers on Quantum Foundations (13)

Authors: Pierre Martin-Dussaud

We discuss the notion of coherent states from three different perspectives: the seminal approach of Schroedinger, the experimental take of quantum optics, and the theoretical developments in quantum gravity. This comparative study tries to emphasise the connections between the approaches, and to offer a coherent short story of the field, so to speak. It may be useful for pedagogical purposes, as well as for specialists of quantum optics and quantum gravity willing to embed their perspective within a wider landscape.

Authors: Indrajit SenAntony Valentini

This is the first of two papers which attempt to comprehensively analyse superdeterministic hidden-variables models of Bell correlations. We first give an overview of superdeterminism and discuss various criticisms of it raised in the literature. We argue that the most common criticism, the violation of `free-will’, is incorrect. We take up Bell’s intuitive criticism that these models are `conspiratorial’. To develop this further, we introduce nonequilibrium extensions of superdeterministic models. We show that the measurement statistics of these extended models depend on the physical system used to determine the measurement settings. This suggests a fine-tuning in order to eliminate this dependence from experimental observation. We also study the signalling properties of these extended models. We show that although they generally violate the formal no-signalling constraints, this violation cannot be equated to physical signalling, in the sense of information transfer between the wings. We therefore suggest that the so-called no-signalling constraints be more appropriately named the marginal-independence constraints. We discuss the mechanism by which marginal-independence is violated in superdeterministic models. We use this to delineate the superdeterministic contribution to the net change in marginals for a hybrid nonlocal superdeterministic model (in nonequilibrium). Lastly, we consider a hypothetical scenario where two experimenters use the apparent-signalling of a superdeterministic model to communicate with each other. This scenario suggests another conspiratorial feature peculiar to superdeterminism. These suggestions are quantitatively developed in the second paper.

Authors: Detlev BuchholzKlaus Fredenhagen

The essence of the path integral method in quantum physics can be expressed in terms of two relations between unitary propagators, describing perturbations of the underlying system. They inherit the causal structure of the theory and its invariance properties under variations of the action. These relations determine a dynamical algebra of bounded operators which encodes all properties of the corresponding quantum theory. This novel approach is applied to non-relativistic particles, where quantum mechanics emerges from it. The method works also in interacting quantum field theories and sheds new light on the foundations of quantum physics.

上午8:40 | Pierre Martin-Dussaud | quant-ph updates on arXiv.org

We discuss the notion of coherent states from three different perspectives: the seminal approach of Schroedinger, the experimental take of quantum optics, and the theoretical developments in quantum gravity. This comparative study tries to emphasise the connections between the approaches, and to offer a coherent short story of the field, so to speak. It may be useful for pedagogical purposes, as well as for specialists of quantum optics and quantum gravity willing to embed their perspective within a wider landscape.

Recently probabilistic hysteresis in isolated Hamiltonian systems of ultracold atoms has been studied in the limit of large particle numbers, where a semiclassical treatment is adequate. The origin of irreversibility in these sweep experiments, where a control parameter is slowly (adiabatically) tuned back and forth, turned out to be a passage blue back and forth across a separatrix (integrable case) or a passage in and out of a chaotic sea in phase space (chaotic case). Here we focus on the full quantum mechanical description of the integrable system and show how the semiclassical results emerge in the limit of large particle numbers. Instead of the crossing of a separatrix in phase space, where classical adiabaticity fails, the origin of irreversibility in the quantum system is a series of avoided crossings of the adiabatic energy levels: they become so close that already for modest particle numbers the change of the external parameter has to be unrealistically slow to reach the quantum adiabatic limit of perfectly reversible evolution. For a slow but finite sweep rate we find a broad regime where the quantum results agree with the semiclassical results, but only if besides the limit $N\to \infty$ an initial ensemble of states is considered, with sufficient initial energy width. For a single initial energy eigenstate we find in contrast that the backward sweep reveals strong quantum effects even for very large particle numbers.

上午8:40 | Detlev Buchholz, Klaus Fredenhagen | quant-ph updates on arXiv.org

The essence of the path integral method in quantum physics can be expressed in terms of two relations between unitary propagators, describing perturbations of the underlying system. They inherit the causal structure of the theory and its invariance properties under variations of the action. These relations determine a dynamical algebra of bounded operators which encodes all properties of the corresponding quantum theory. This novel approach is applied to non-relativistic particles, where quantum mechanics emerges from it. The method works also in interacting quantum field theories and sheds new light on the foundations of quantum physics.

上午8:40 | Brandon Elford, Petr Lisonek | quant-ph updates on arXiv.org

For the first time we construct an infinite family of Kochen-Specker sets in a space of fixed dimension, namely in R^4. While most of the previous constructions of Kochen-Specker sets have been based on computer search, our construction is analytical and it comes with a short, computer-free proof.

上午8:40 | Andrzej Góźdź, Marek Góźdź | quant-ph updates on arXiv.org

In quantum mechanics, time is introduced as a non-measurable quantity, as there is no possibility to build a hermitian operator canonically conjugated to the Hamiltonian. We cannot have, therefore, the time operator, which means that the temporal structure of the evolution of quantum systems is ill-defined. We present an extension to the model, in which the time evolution is based on the projection postulate rather than the unitary operator. This approach is in agreement with all other aspects of quantum mechanics and allows to discuss time as an observable. Using this framework we present a description of the temporal double-slit experiment in which a~single particle interferes with itself from a different instant of time. Such behaviour has already been observed experimentally but lacked a consistent theoretical explanation.

上午8:40 | Raphael Bousso, Fernando Quevedo, Steven Weinberg | quant-ph updates on arXiv.org

Joseph Polchinski (1954-2018), one of the the leading theoretical physicists of the past 50 years, was an exceptionally broad and deep thinker. He made fundamental contributions to quantum field theory, advancing the role of the renormalization group, and to cosmology, addressing the cosmological constant problem. Polchinski’s work on D-branes revolutionized string theory and led to the discovery of a nonperturbative quantum theory of gravity. His recent, incisive reformulation of the black hole information paradox presents us with a profound challenge. Joe was deeply devoted to his family, a beloved colleague and advisor, an excellent writer, and an accomplished athlete.

上午8:40 | ScienceDirect Publication: Physics ReportsScienceDirect RSShttps://www.sciencedirect.com/journal/physics-reportsRSS for NodeTue, 23 Jul 2019 10:02:48 GMTCopyright © 2019 Elsevier B.V. All rights reservedRapid solidification as non-ergodic phenomenonPublication date: 20 July 2019Source: Physics Reports, Volume 818Author(s): P.K. Galenko, D. JouAbstractRapid solidification is a relevant physical phenomenon in material sciences, whose theoretical analysis requires going beyond the limits of local equilibrium statistical physics and thermodynamics and, in particular, taking account of ergodicity breaking and of generalized formulation of thermodynamics. The ergodicity breaking is related to the time symmetry breaking and to the presence of some kinds of fluxes and gradient flows making that an average of microscopic variables along time is different than an average over some chosen statistical ensemble. In fast processes, this is due, for instance, to the fact that the system has no time enough to explore the who

Publication date: Available online 26 March 2020

Source: Physics Reports

Author(s): Masahito Yamazaki

Authors: Fay DowkerNazireen ImambaccusAmelia OwensRafael SorkinStav Zalel

We propose a manifestly covariant framework for causal set dynamics. The framework is based on a structure, dubbed covtree, which is a partial order on certain sets of finite, unlabeled causal sets. We show that every infinite path in covtree corresponds to at least one infinite, unlabeled causal set. We show that transition probabilities for a classical random walk on covtree induce a classical measure on the $\sigma$-algebra generated by the stem sets.

Authors: Thiago Guerreiro

We discuss the quantum mechanical description of a gravitational wave interacting with a cavity electromagnetic field. Quantum fluctuations of the gravitational vacuum induce squeezing in the optical field. Moreoever, this squeezing experiences revivals, which are a purely quantum effect. Measuring these “gravitationally induced revivals”, altought out of reach from experiments, would provide evidence on the quantum nature of gravity. We also discuss the quantum mechanical treatment of the interaction between coherent and squeezed gravitational wave states and a gravity-wave detector. In the case of a coherent gravitational wave, we reproduce the result from the classical theory with a quantum mechanical calculation. The case of a squeezed gravity wave is not calculable within the classical theory, and could provide evidence on the quantum nature of gravity.

Authors: Henning BostelmannChristopher J. FewsterMaximilian H. Ruep

In 1993, Sorkin argued that, for most local observables in quantum field theory, an ideal measurement can result in superluminal signalling and is therefore considered impossible. We analyse his signalling protocol in a recently proposed measurement scheme for quantum field theory. Here a measurement of a system is described by coupling it to a probe, this coupling importantly being local in space and time. In this setting, we show that measurements do not exhibit superluminal signalling; hence Sorkin’s impossible measurements can only be performed using impossible (non-local) apparatus.

Authors: Özgür ÖkcüChristian CordaEkrem Aydiner

Considering the modified entropy-area relation from DSR-GUP (Doubly special relativity-Generalized uncertainity principle), we obtain the modified Friedmann equations from the first law of thermodynamics at apparent horizon. Due to the importance of GUP at Planck scale, we investigate the Friedmann equations and show the maximum energy density \r{ho} at Planck scale. Since GUP implies a minimal length, we find a minimum apparent horizon which has a potential to remove the Big Bang singularity. Furthermore, we analyse the effects of DSR-GUP on deceleration parameter q for the equation of state p = {\omega}\r{ho} and the flat case. Finally, we check the validity of the generalized second law (GSL) of thermodynamics and show that it is valid all eras of the Universe for any spatial curvature.

2020年3月27日 星期五 下午6:00 | E. R. Moan, R. A. Horne, T. Arpornthip, Z. Luo, A. J. Fallon, S. J. Berl, and C. A. Sackett | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): E. R. Moan, R. A. Horne, T. Arpornthip, Z. Luo, A. J. Fallon, S. J. Berl, and C. A. Sackett

We describe a Sagnac interferometer suitable for rotation sensing, implemented using an atomic Bose-Einstein condensate confined in a harmonic magnetic trap. The atom wave packets are split and recombined by standing-wave Bragg lasers, and the trapping potential steers the packets along circular tra…

[Phys. Rev. Lett. 124, 120403] Published Fri Mar 27, 2020

2020年3月27日 星期五 上午8:00 | Latest Results for Foundations of Physics

Abstract

There are two types of fluctuations in the quantum vacuum: type 1 vacuum fluctuations are on shell and can interact with matter in specific, limited ways that have observable consequences; type 2 vacuum fluctuations are off shell and cannot interact with matter. A photon will polarize a type 1, bound, charged lepton–antilepton vacuum fluctuation in much the same manner that it would polarize a dielectric, suggesting the method used here for calculating the permittivity \(\epsilon _{0}\) of the vacuum. In a model that retains only leading terms, \(\epsilon _{0} \cong (6\mu _{0}/\pi )(8e^{2}/\hbar )^{2}= 9.10\times 10^{-12}\) C/(Vm). The calculated value for \(\epsilon _{0}\) is 2.7% more than the accepted value. The permittivity of the vacuum, in turn, determines the speed c of light in the vacuum. Since the vacuum is at rest with respect to every inertial frame of reference, c is the same in every inertial reference frame.

2020年3月26日 星期四 上午8:00 | Latest Results for Synthese

Abstract

According to ‘Strong Composition as Identity’ (SCAI), if an entity is composed of a plurality of entities, it is identical to them. As it has been argued in the literature, SCAI appears to give rise to some serious problems which seem to suggest that SCAI-theorists should take their plural quantifier to be governed by some ‘weak’ plural comprehension principle and, thus, ‘exclude’ some kinds of pluralities from their plural ontology. The aim of this paper is to argue that, contrary to what may appear at first sight, the assumption of a weak plural comprehension principle is perfectly compatible with plural logic and the common uses of plural quantification. As I aim to show, SCAI-theorists can simply claim that their theory must be understood as formulated by means of the most ‘joint-carving’ plural quantifier, thus leaving open the possibility of other, less joint-carving, ‘unrestricted’ plural quantifiers. In the final part of the paper I will also suggest that SCAI-theorists should not only allow for singular quantification over pluralities of entities, but also for plural quantification over ‘super-pluralities’ of entities.

2020年3月25日 星期三 下午12:05 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
List, Christian (2020) The many-worlds theory of consciousness. [Preprint]
2020年3月24日 星期二 下午1:27 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Lam, Vincent and Wuthrich, Christian (2020) Spacetime functionalism from a realist perspective. [Preprint]
2020年3月23日 星期一 下午6:00 | Sreekanth K. Manikandan, Deepak Gupta, and Supriya Krishnamurthy | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Sreekanth K. Manikandan, Deepak Gupta, and Supriya Krishnamurthy

We provide a strategy for the exact inference of the average as well as the fluctuations of the entropy production in nonequilibrium systems in the steady state, from the measurements of arbitrary current fluctuations. Our results are built upon the finite-time generalization of the thermodynamic un…

[Phys. Rev. Lett. 124, 120603] Published Mon Mar 23, 2020

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