Weekly Papers on Quantum Foundations (37)

This is a list of this week’s papers on quantum foundations published in various journals or uploaded to preprint servers such as arxiv.org and PhilSci Archive.

On the meaning of locality: the overlapping assumptions. (arXiv:1509.03301v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-9-12 7:38am GMT

Authors: Afshin ShafieeFarhad Taher Ghahramani

We examine the locality assumption of Bell’s theorem in three steps of EPRB experiment. Depending on the context, locality is embodied in the conditions of separability, local causality, factorizability, relativistic causality, and non-contextuality. We show that separability, characterized by the constraint of zero covariance, is equivalent to local causality which leads to factorizability through the measurement process. Factorizability is the conjunction of parameter independence and outcome independence. It is commonly believed that relativistic causality is equivalent to parameter independence, which is satisfied by quantum mechanics. According to our approach, however, this is unjustified due to the second step analysis of EPRB experiment, including the measurement on the first particle. We define non-contextuality based on preparation procedure and measurement process. Preparation-based non-contextuality is an independent assumption, but non-locality within the framework of a separable model can be interpreted as measurement-based contextuality. Finally, we show that any fundamental theory consistent with quantum mechanics, should refute outcome independence in its framework of description.

Comment on Carlo Rovelli’s “An argument against the realistic interpretation of the wave function”. (arXiv:1508.06895v2 [quant-ph] CROSS LISTED)

gr-qc updates on arXiv.org

on 2015-9-12 7:35am GMT

Authors: H. Dieter Zeh

Rovelli’s argument against the realistic interpretation of quantum states and in favor of an ontology of quantum events is refuted.

[Perspective] Interference of atomic clocks

Science: Current Issue

on 2015-9-11 12:00am GMT

When de Broglie predicted that we need to associate a periodic phenomenon with any isolated portion of matter or energy (1), this idea became the basis of Schrödinger’s wave equation and modern matter-wave interferometry. It has stood the test of time and inspired intriguing discussions on the relation between quantum physics, classicality (2), and general relativity theory (GRT) (3–5). It also inspired the recent work on page 1205 of this issue by Margalit et al. (6), who demonstrated that the internal clock of a delocalized atom can be used as a witness of the atom’s path through a matter-wave interferometer. The study shows Bohr’s complementarity principle in action and how dephasing in an external potential may mimic “classicality” even though the underlying quantum correlations can be erased and reversed. Authors: Markus Arndt, Christian Brand

[Report] A self-interfering clock as a “which path” witness

Science: Current Issue

on 2015-9-11 12:00am GMT

In Einstein’s general theory of relativity, time depends locally on gravity; in standard quantum theory, time is global—all clocks “tick” uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories: a self-interfering clock, comprising two atomic spin states. We prepare the clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the clock wave packets “tick” at different rates, to simulate a gravitational time lag, the clock time along each path yields “which path” information, degrading the pattern’s visibility. In contrast, in standard interferometry, time cannot yield “which path” information. This proof-of-principle experiment may have implications for the study of time and general relativity and their impact on fundamental effects such as decoherence and the emergence of a classical world. Authors: Yair Margalit, Zhifan Zhou, Shimon Machluf, Daniel Rohrlich, Yonathan Japha, Ron Folman

Black Hole with Quantum Potential. (arXiv:1509.02495v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-9-10 12:28am GMT

Authors: Ahmed Farag AliMohammed M. Khalil

In this work, we investigate black hole (BH) physics in the context of quantum corrections. These quantum corrections were introduced recently by replacing classical geodesics with quantal (Bohmian) trajectories and hence form a quantum Raychaudhuri equation (QRE). From the QRE, we derive a modified Schwarzschild metric, and use that metric to investigate BH singularity and thermodynamics. We find that these quantum corrections change the picture of Hawking radiation greatly when the size of BH approaches the Planck scale. They prevent the BH from total evaporation, predicting the existence of a quantum BH remnant, which introduces a possible resolution for the catastrophic behavior of Hawking radiation as the BH mass approaches zero. It also ameliorates the black hole singularity and the information loss problem.

Review on Generalized Uncertainty Principle. (arXiv:1509.02436v1 [physics.gen-ph])

gr-qc updates on arXiv.org

on 2015-9-10 12:28am GMT

Authors: Abdel Nasser TawfikAbdel Magied Diab (Egyptian Ctr. Theor. Phys., Cairo, WLCAPP, Cairo)

Based on string theory, black hole physics, doubly special relativity and some “thought” experiments, minimal distance and/or maximum momentum are proposed. As alternatives to the generalized uncertainty principle (GUP), the modified dispersion relation, the space noncommutativity, the Lorentz invariance violation, and the quantum-gravity-induced birefringence effects are summarized. The origin of minimal measurable quantities and the different GUP approaches are reviewed and the corresponding observations are analysed. Bounds on the GUP parameter are discussed and implemented in understanding recent PLANCK observations on the cosmic inflation. The higher-order GUP approaches predict minimal length uncertainty with and without maximum momenta.

Experiments testing macroscopic quantum superpositions must be slow. (arXiv:1509.02408v1 [quant-ph])

gr-qc updates on arXiv.org

on 2015-9-10 12:28am GMT

Authors: Andrea MariGiacomo De PalmaVittorio Giovannetti

We consider a thought experiment where the preparation of a macroscopically massive or charged particle in a quantum superposition and the associated dynamics of a distant test particle apparently allow for superluminal communication. We give a solution to the paradox which is based on the following fundamental principle: any local experiment, discriminating a coherent superposition from an incoherent statistical mixture, necessarily requires a minimum time proportional to the mass (or charge) of the system. For a charged particle, we consider two examples of such experiments, and show that they are both consistent with the previous limitation. In the first, the measurement requires to accelerate the charge, that can entangle with the emitted photons. In the second, the limitation can be ascribed to the quantum vacuum fluctuations of the electromagnetic field. On the other hand, when applied to massive particles our result provides an indirect evidence for the existence of gravitational vacuum fluctuations and for the possibility of entangling a particle with quantum gravitational radiation.

Inconstant Planck’s constant. (arXiv:1509.02107v1 [quant-ph] CROSS LISTED)

hep-th updates on arXiv.org

on 2015-9-10 12:28am GMT

Authors: Gianpiero ManganoFedele LizziAlberto Porzio

Motivated by the Dirac idea that fundamental constant are dynamical variables and by conjectures on quantum structure of spacetime at small distances, we consider the possibility that Planck constant $\hbar$ is a time depending quantity, undergoing random gaussian fluctuations around its measured constant mean value, and with a typical correlation timescale $\tau$. We consider the case of propagation of a free particle and a one–dimensional harmonic oscillator coherent state, and show that the time evolution in both cases is different from the standard behaviour. Finally, we discuss how interferometric experiments or exploiting coherent electromagnetic fields in a cavity may put effective bounds on the value of $\tau$.

From the Kochen-Specker Theorem to Noncontextuality Inequalities without Assuming Determinism

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

on 2015-9-09 2:00pm GMT

Author(s): Ravi Kunjwal and Robert W. Spekkens

The Kochen-Specker theorem demonstrates that it is not possible to reproduce the predictions of quantum theory in terms of a hidden variable model where the hidden variables assign a value to every projector deterministically and noncontextually. A noncontextual value assignment to a projector is on…

 

[Phys. Rev. Lett. 115, 110403] Published Wed Sep 09, 2015

Can Bohmian mechanics be made background independent?

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

on 2015-9-09 12:36pm GMT

Publication date: Available online 5 September 2015
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Antonio Vassallo
The paper presents an inquiry into the question regarding the compatibility of Bohmian mechanics, intended as a non-local theory of moving point-like particles, with background independence. This issue is worth being investigated because, if the Bohmian framework has to be of some help in developing new physics, it has to be compatible with the most well-established traits of modern physics, background independence being one of such traits. The paper highlights the fact that the notion of background independence in the context of spacetime physics is slippery and interpretation-laden. It is then suggested that the best-matching framework developed by Julian Barbour might provide a robust enough meaning of background independence. The structure of Bohmian dynamics is evaluated against this framework, reaching some intermediate results that speak in favor of the fact that Bohmian mechanics can be made background independent.

Characterizing common cause closedness of quantum probability theories

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

on 2015-9-09 12:36pm GMT

Publication date: Available online 8 September 2015
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Yuichiro Kitajima, Miklós Rédei
We prove new results on common cause closedness of quantum probability spaces, where by a quantum probability space is meant the projection lattice of a non-commutative von Neumann algebra together with a countably additive probability measure on the lattice. Common cause closedness is the feature that for every correlation between a pair of commuting projections there exists in the lattice a third projection commuting with both of the correlated projections and which is a Reichenbachian common cause of the correlation. The main result we prove is that a quantum probability space is common cause closed if and only if it has at most one measure theoretic atom. This result improves earlier ones published in Gyenis and Rédei (2014). The result is discussed from the perspective of status of the Common Cause Principle. Open problems on common cause closedness of general probability spaces ( L , ϕ ) are formulated, where L is an orthomodular bounded lattice and ϕ is a probability measure on L .

Quantum States as Objective Informational Bridges

Latest Results for Foundations of Physics

on 2015-9-09 12:00am GMT

Abstract

A quantum state represents neither properties of a physical system nor anyone’s knowledge of its properties. The important question is not what quantum states represent but how they are used—as informational bridges. Knowing about some physical situations (its backing conditions), an agent may assign a quantum state to form expectations about other possible physical situations (its advice conditions). Quantum states are objective: only expectations based on correct state assignments are generally reliable. If a quantum state represents anything, it is the objective probabilistic relations between its backing conditions and its advice conditions. This paper offers an account of quantum states and their function as informational bridges, in quantum teleportation and elsewhere.

On structural accounts of model-explanations

Latest Results for Synthese

on 2015-9-09 12:00am GMT

Abstract

The focus in the literature on scientific explanation has shifted in recent years towards model-based approaches. In recent work, Alisa Bokulich has argued that idealization has a central role to play in explanation. Bokulich claims that certain highly-idealized, structural models can be explanatory, even though they are not considered explanatory by causal, mechanistic, or covering law accounts of explanation. This paper focuses on Bokulich’s account in order to make the more general claim that there are problems with maintaining that a structural criterion can capture the way that highly-idealized models explain. This paper examines Bokulich’s claim that the structural model explanation of quantum wavefunction scarring, featuring semiclassical mechanics, is deeper than the explanation provided by the local quantum model. The challenge for Bokulich is to show that the semiclassical model answers a wider range of w-questions (what-if-things-had-been-different-questions), as this is her method of assessing structural information. I look at two reasonable approaches employing w-questions, and I argue that neither approach is ultimately satisfactory. Because structural similarity has preferences for more fundamental models, I argue that the local quantum model provides explanations that at least as deep as the semiclassical ones. The criterion either wrongly identifies all models as explanatory, or prefers models from fundamental theory. Either way, it cannot capture the way that highly-idealized models explain.

Dark energy from the gravity vacuum

Classical and Quantum Gravity – latest papers

on 2015-9-08 11:00pm GMT

We propose a new solution to the cosmological constant problem building on a nonperturbative quantum theory of gravity with torsional instantons. These pseudoparticles, which were recently found to exist in a first order formulation of Giddings?Strominger axionic gravity, carry nontrivial Nieh?Yan topological charge. The nonperturbative ground state as generated due to tunneling effects is shown to be stable under quantum fluctuations. Within this framework, the associated vacuum angle, namely the Barbero?Immirzi topological parameter, gets fixed to a numerical value determined by the Hubble constant.

 

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