Weekly Papers on Quantum Foundations (52)

Relativity and Quantum Theory: Under the Spell of Today’s Paradigms. (arXiv:2312.17693v1 [physics.hist-ph]) 

from physics.hist-ph by Stefan WeigertMon Jan 01 2024 11:29:57 (5 hours)# 1.

Thomas S. Kuhn interprets the development of the (natural) sciences as a specific dynamical process. Periods of piecemeal growth of knowledge based on widely accepted paradigms are interrupted by bursts of revolutionary changes which lead to new paradigms incommensurate with the earlier ones. This process is briefly illustrated by recalling the changes to classical physics brought about by Einstein’s theory of relativity on the one hand, and by quantum theory on the other. Both theories represent fundamental paradigms of contemporary physics. They appear unshakable to the working physicist but according to Kuhn their paradigmatic status is of a temporary nature only. Does Kuhn’s framework help us to identify potential future revolutions?

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Decomposition of State Spaces into Subobjects in Quantum Field Theory. (arXiv:2312.17275v1 [quant-ph]) 

from quant-ph by Pierre Gosselin (IF)Mon Jan 01 2024 11:29:57 (5 hours)# 2.

This paper introduces a comprehensive formalism for decomposing the state space of a quantum field into several entangled subobjects, i.e., fields generating a subspace of states. Projecting some of the subobjects onto degenerate background states reduces the system to an effective field theory depending on parameters representing the degeneracies. Notably, these parameters are not exogenous. The entanglement among subobjects in the initial system manifests as an interrelation between parameters and non-projected subobjects. Untangling this dependency necessitates imposing linear first-order equations on the effective field. The geometric characteristics of the parameter spaces depend on both the effective field and the background of the projected subobjects. The system, governed by arbitrary variables, has no dynamics, but the projection of some subobjects can be interpreted as slicing the original state space according to the lowest eigenvalues of a parameter-dependent family of operators. The slices can be endowed with amplitudes similar to some transitions between each other, contingent upon these eigenvalues. Averaging over all possible transitions shows that the amplitudes are higher for maps with increased eigenvalue than for maps with decreasing eigenvalue.

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Emerging Entanglement on Network Histories. (arXiv:2312.17313v1 [hep-th]) 

from quant-ph by Cecilia Giavoni, Stefan Hofmann, Maximilian KoeglerMon Jan 01 2024 11:29:52 (5 hours)# 3.

We show that quantum fields confined to Lorentzian histories of freely falling networks in Minkowski spacetime probe entanglement properties of vacuum fluctuations that extend unrestricted across spacetime regions. Albeit instantaneous field configurations are localised on one-dimensional edges, angular momentum emerges on these network histories and establishes the celebrated area scaling of entanglement entropy.

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Vacuum Energy from Qubit Entropy. (arXiv:2312.17317v1 [hep-th]) 

from quant-ph by Gonçalo M. Quinta, Antonino FlachiMon Jan 01 2024 11:29:51 (5 hours)# 4.

We develop a non-conventional description of the vacuum energy in quantum field theory in terms of quantum entropy. Precisely, we show that the vacuum energy of any non-interacting quantum field at zero temperature is proportional to the quantum entropy of the qubit degrees of freedom associated with virtual fluctuations. We prove this for fermions first, and then extend the derivation to quanta of any spin. Finally, we use these results to obtain the first law of thermodynamics for a non-interacting quantum vacuum at zero temperature.

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Quantum measure as a necessary ingredient in quantum gravity and modified gravities. (arXiv:2312.17546v1 [gr-qc]) 

from gr-qc by Vladimir Dzhunushaliev, Vladimir FolomeevMon Jan 01 2024 11:29:48 (5 hours)# 5.

We suggest commutation relations for a quantum measure. In one version of these relations, the right-hand side takes account of the presence of curvature of space; in the simplest case, this yields the action of general relativity. We consider the cases of the quantization of the measure on spaces of constant curvature and show that in this case the commutation relations for the quantum measure are analogues of commutation relations in loop quantum gravity. It is assumed that, in contrast to loop quantum gravity, a triangulation of space is a necessary trick for quantizing such a nonlocal quantity like a measure; in doing so, the space remains a smooth manifold. We consider the self-consistent problem of the interaction of the quantum measure and classical gravitation. It is shown that this inevitably leads to the appearance of modified gravities. Also, we consider the problem of defining the Euler-Lagrange equations for a matter field in the background of a space endowed with quantum measure.

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PT-symmetric quantum mechanics. (arXiv:2312.17386v1 [quant-ph]) 

from quant-ph by Carl M. Bender, Daniel W. HookMon Jan 01 2024 11:29:46 (5 hours)# 6.

It is generally assumed that a Hamiltonian for a physically acceptable quantum system (one that has a positive-definite spectrum and obeys the requirement of unitarity) must be Hermitian. However, a PT-symmetric Hamiltonian can also define a physically acceptable quantum-mechanical system even if the Hamiltonian is not Hermitian. The study of PT-symmetric quantum systems is a young and extremely active research area in both theoretical and experimental physics. The purpose of this Review is to provide established scientists as well as graduate students with a compact, easy-to-read introduction to this field that will enable them to understand more advanced publications and to begin their own theoretical or experimental research activity. The ideas and techniques of PT symmetry have been applied in the context of many different branches of physics. This Review introduces the concepts of PT symmetry by focusing on elementary one-dimensional PT-symmetric quantum and classical mechanics and relies in particular on oscillator models to illustrate and explain the basic properties of PT-symmetric quantum theory.

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On Wigdersons’ approach to the uncertainty principle. (arXiv:2312.17438v1 [math.FA]) 

from quant-ph by Nuno Costa Dias, Franz Luef, João Nuno PrataMon Jan 01 2024 11:29:43 (5 hours)# 7.

We revisit the uncertainty principle from the point of view suggested by A. Wigderson and Y. Wigderson. This approach is based on a primary uncertainty principle from which one can derive several inequalities expressing the impossibility of a simultaneous sharp localization in time and frequency. Moreover, it requires no specific properties of the Fourier transform and can therefore be easily applied to all operators satisfying the primary uncertainty principle. A. Wigderson and Y. Wigderson also suggested many generalizations to higher dimensions and stated several conjectures which we address in the present paper. We argue that we have to consider a more general primary uncertainty principle to prove the results suggested by the authors. As a by-product we obtain some new inequalities akin to the Cowling-Price uncertainty principle and derive the entropic uncertainty principle from the primary uncertainty principles.

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Towards an experimental proof of the magnonic Aharonov-Casher effect 

from APS – editor suggestions by Rostyslav O. Serha, Vitaliy I. Vasyuchka, Alexander A. Serga, and Burkard HillebrandsFri Dec 29 2023 05:00:00 (3 days)# 8.

Author(s): Rostyslav O. Serha, Vitaliy I. Vasyuchka, Alexander A. Serga, and Burkard Hillebrands

The Aharonov-Casher effect is the accumulation of the wave function phase when a particle with magnetic moment passes through an electric field. This phenomenon is observed for real particles and predicted for quasiparticles such as magnons. Here, the authors investigate the impact of a strong electric field on the phase of dipolar spin waves exited in a ferromagnetic yttrium iron garnet (YIG) film and report the experimental results in favor of the magnonic Aharonov-Casher effect.

[Phys. Rev. B 108, L220404] Published Fri Dec 29, 2023

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Quantum probability from temporal structure. (arXiv:2112.10929v5 [quant-ph] UPDATED) 

from physics.hist-ph by Michael RidleyWed Dec 27 2023 12:05:48 (5 days)# 9.

The Born probability measure describes the statistics of measurements in which observers self-locate themselves in some region of reality. In $\psi$-ontic quantum theories, reality is directly represented by the wavefunction. We show that quantum probabilities may be identified with fractions of a universal multiple-time wavefunction containing both causal and retrocausal temporal parts. This wavefunction is defined in an appropriately generalized history space on the Keldysh time contour. Our deterministic formulation of quantum mechanics replaces the initial condition of standard Schr\”odinger dynamics with a network of `fixed points’ defining quantum histories on the contour. The Born measure is derived by summing up the wavefunction along these histories. We then apply the same technique to the derivation of the statistics of measurements with pre- and post-selection.

Mulder, Ruward A. and Read, James (2023) Is spacetime curved? Assessing the underdetermination of general relativity and teleparallel gravity. [Preprint]

Wolf, William J. and Read, James and Vigneron, Quentin (2023) The Non-Relativistic Geometric Trinity of Gravity. [Preprint]

Ovidiu Cristinel, Stoica (2023) Does a computer think if no one is around to see it? [Preprint]

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