Weekly Papers on Quantum Foundations (1)

上午9:05 | Armin Tavakoli, Nicolas Gisin | quant-ph updates on arXiv.org

The Platonic solids is the name traditionally given to the five regular convex polyhedra, namely the tetradron, the octahedron, the cube, the icosahedron and the dodecahedron. Perhaps strongly boosted by the towering historical influence of their namesake, these beautiful solids have, in well over two millenia, transcended traditional boundaries and entered the stage in a range of disciplines. Examples include natural philosophy and mathematics from classical antiquity, scientific modeling during the days of the european scientific revolution and visual arts ranging from the renaissance to modernity. Motivated by mathematical beauty and a rich history, we consider the Platonic solids in the context of modern quantum mechanics. Specifically, we construct Bell inequalities whose maximal violations are achieved with measurements pointing to the vertices of the Platonic solids. These Platonic Bell inequalities are constructed only by inspecting the visible symmetries of the Platonic solids. We also construct Bell inequalities for more general polyhedra and find a Bell inequality that is more robust to noise than the celebrated Clauser-Horne-Shimony-Holt Bell inequality. Finally, we elaborate on the tension between mathematical beauty, which was our initial motivation, and experimental friendliness, which is necessary in all empirical sciences.

上午9:05 | Giuseppe Giuliani | quant-ph updates on arXiv.org

A critical reconsideration of the EPR (Einstein-Podolsky-Rosen) paper shows that the EPR argument can be developed without using the concept of `element of physical reality’, thus eliminating any philosophical element in the logical chains of the paper. Deprived of its philosophical ornament, the EPR argument plainly reduces to require what quantum mechanics can not do: to assign definite values to two incompatible physical quantities. Hidden variables theories built up according to Bell – type theorems are formulated on the basis of the assumption that the locality condition implies the statistical independence between two measurements space – like separated. This assumption is valid only with the additional one that statistical dependence between two measurements requires a causal connection between them. This additional assumption rules out the possibility that statistical dependence may due to an intrinsic property of the physical system under study. Therefore, hidden variables theories are built up with a restriction which leads them to be disproved by experiment. Quantum mechanical non – locality, invoked for describing EPR – type experiments, is strictly connected to the hypothesis (NDV hypothesis) according to which the twin photons of entangled pairs do not have a definite polarization before measurements. Both hypotheses are used only for describing EPR experiments and not for making predictions. Therefore, they can be dropped without reducing the predictive power of quantum mechanics concerning entangled photons pairs. Furthermore, both hypotheses can be experimentally tested by a modification of a standard experimental apparatus designed for studying entangled photons pairs.

Authors: Christian de Ronde

In this work we analyze the deep link between the 20th Century positivist re-foundation of physics and the famous measurement problem of quantum mechanics. We attempt to show why this is not an “obvious” nor “self evident” problem for the theory of quanta, but rather a direct consequence of the empirical-positivist understanding of physical theories when applied to the orthodox quantum formalism. In contraposition, we discuss a representational realist account of both physical ‘theories’ and ‘measurement’ which goes back to the works of Einstein, Heisenberg and Pauli. After presenting a critical analysis of Bohr’s definitions of ‘measurement’ we continue to discuss the way in which several contemporary approaches to QM –such as decoherence, modal interpretations and QBism– remain committed to Bohr’s general methodology. Finally, in order to expose the many inconsistencies present within the (empirical-positivist) presuppositions responsible for creating the quantum measurement problem, we show how through these same set of presuppositions it is easy to derive a completely analogous paradox for the case of classical mechanics.

Authors: A. Y. Klimenko

This work reviews the understanding of the direction of time introduced by Hans Reichenbach, including the fundamental relation of the perceived flow of time to the second law of thermodynamics (i.e. the Boltzmann time hypothesis), and the principle of parallelism of entropy increase. An example of a mixing process with quantum effects, which is advanced here in conjunction with Reichenbach’s ideas, indicates the existence of a presently unknown mechanism that reflects global conditions prevailing in the universe and enacts the direction of time locally (i.e. the “time primer”). The possibility of experimental detection of the time primer is also discussed: if the time primer is CPT-invariant, its detection may be possible in high-energy experiments under the current level of technology.

Authors: Run-Qiu YangH. Lu

For static black holes in Einstein gravity, if matter fields satisfy a few general conditions, we conjecture that three characteristic parameters about the spatial size of black holes, namely the outermost photon sphere area $A_{\text{ph,out}}$, the corresponding shadow area $A_{\text{sh,out}}$ and the horizon area $A_{H}$ satisfy a series of universal inequalities $9A_{H}/4\leq A_{\text{ph,out}}\leq A_{\text{sh,out}}/3\leq 36\pi M^2$, where $M$ is the ADM mass. We present a complete proof in the spherically symmetric case and some pieces of evidence to support it in general static cases. We also discuss the properties of the photon spheres in general static spacetimes and show that, similar to horizon, photon spheres are also conformal invariant structures of the spacetimes.

Authors: Markus RummelC.P. Burgess

We show how Event Horizon Telescope (EHT) observations of the supermassive object at the center of M87 can constrain deviations from General Relativity (GR) in a relatively model-independent way. We focus on the class of theories whose deviations from GR modify black holes into alternative compact objects whose properties approach those of an ordinary black hole sufficiently far from the would-be event horizon. We examine this class for two reasons: ($i$) they tend to reproduce black-hole expectations for astrophysical accretion disks (and so do not undermine the evidence linking black holes to active galactic nuclei); ($ii$) they lend themselves to a robust effective-field-theory treatment that expands in powers of $\ell/r$, where $\ell$ is the fundamental length scale that sets the distance over which deviations from GR are significant and $r$ is a measure of distance from the would-be horizon. At leading order the observational impact of these types of theories arise as modifications to the transmission and reflection coefficients of modes as they approach the horizon. We show how EHT observations can constrain this reflection coefficient, assuming only that the deviations from GR are small enough to be treated perturbatively. Our preliminary analysis indicates that such reflection coefficients can already be constrained to be less than of order 10$\%$, and so can rule out some benchmark cases used when seeking black-hole echoes. The precise bounds depend on the black hole spin, as well as on detailed properties of the reflection coefficient (such as its dependence on angular direction).

Authors: Markus Pössel

The gravitational time delay of light, also called the Shapiro time delay, is one of the four classical tests of Einstein’s theory of general relativity. This article derives the Newtonian version of the Shapiro time delay from Einstein’s principle of equivalence and the Newtonian description of gravity, in a manner that is accessible to undergraduate students and advanced high-school students. The derivation can be used as a pedagogical tool, similar to the way that simplified derivations of the gravitational deflection of light are used in teaching about general relativity without making use of the more advanced mathematical concepts. Next, we compare different general-relativistic derivations of the Shapiro time delay from the Schwarzschild metric, which leads to an instructive example for the challenges of formulating the post-Newtonian limit of Einstein’s theory. The article also describes simple applications of the time delay formula to observations within our solar system, as well as to binary pulsars.

Authors: S. JalalzadehA. J. S. Capistrano

The causal stochastic interpretation of relativistic quantum mechanics has the problems of superluminal velocities, motion backward in time and the incorrect non-relativistic limit. In this paper, according to the original ideas of de Broglie, Bohm and Takabayasi, we have introduced simultaneous quantum mass and quantum metric of curved spacetime to obtain a correct relativistic theory free of mentioned problems. \keywords{Bohmian mechanics; Klein-Gordon equation; quantum conformal transformations.

2020年1月2日 星期四 下午6:00 | S. Barbarino, J. Yu, P. Zoller, and J. C. Budich | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): S. Barbarino, J. Yu, P. Zoller, and J. C. Budich

A method to efficiently prepare topological states in ultracold atoms is formulated.


[Phys. Rev. Lett. 124, 010401] Published Thu Jan 02, 2020

2020年1月2日 星期四 上午8:00 | Latest Results for Synthese

Abstract

Typically, a less fundamental theory, or structure, emerging from a more fundamental one is an example of synchronic emergence. A model (and the physical state it describes) emerging from a prior model (state) upon which it nevertheless depends is an example of diachronic emergence. The case of spacetime emergent from quantum gravity and quantum cosmology challenges these two conceptions of emergence. Here, I propose two more-general conceptions of emergence, analogous to the synchronic and diachronic ones, but which are potentially applicable to the case of emergent spacetime: an inter-level, hierarchical conception, and an intra-level, ‘flat’ conception. I then explore whether, and how, these ideas may be applicable in the case of several putative examples of relativistic spacetime emergent from the non-spatiotemporal structures described by different approaches to quantum gravity, and of spacetime emergent from a non-spatiotemporal ‘big bang’ state according to different examples of quantum cosmology.

2020年1月2日 星期四 上午8:00 | Latest Results for Foundations of Physics

Abstract

We show that in a dilute gas the wave function’s spreading is limited by scattering off other particles. This shows that quantum mechanics can be consistent with the kinetic theory of gases.

2020年1月1日 星期三 下午12:03 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Serafino, Loris (2019) DEMYSTIFYING LANFORD’S THEOREM. [Preprint]
2020年1月1日 星期三 上午11:57 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Howson, Colin (2019) Beyond Finite Additivity. [Preprint]
2019年12月28日 星期六 下午9:05 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Malament, David Notes on Geometry and Spacetime (Version 7.2). UNSPECIFIED.

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