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.

Multiplicity in Everett׳s interpretation of quantum mechanics

on 2015-10-27 9:45am GMT

Publication date: Available online 23 October 2015

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

Author(s): Louis Marchildon

Everett׳s interpretation of quantum mechanics was proposed to avoid problems inherent in the prevailing interpretational frame. It assumes that quantum mechanics can be applied to any system and that the state vector always evolves unitarily. It then claims that whenever an observable is measured, all possible results of the measurement exist. This notion of multiplicity has been understood in different ways by proponents of Everett׳s theory. In fact the spectrum of opinions on various ontological questions raised by Everett׳s approach is rather large, as we attempt to document in this critical review. We conclude that much remains to be done to clarify and specify Everett׳s approach.

Presenting Nonreflexive Quantum Mechanics: Formalism and Metaphysics

PhilSci-Archive: No conditions. Results ordered -Date Deposited.

on 2015-10-26 3:51pm GMT

Krause, Décio and Arenhart, Jonas R. B. (2015) Presenting Nonreflexive Quantum Mechanics: Formalism and Metaphysics. [Preprint]

“Formal” vs. “Empirical” Approaches to Quantum-Classical Reduction

PhilSci-Archive: No conditions. Results ordered -Date Deposited.

on 2015-10-25 3:01am GMT

Rosaler, Joshua (2015) “Formal” vs. “Empirical” Approaches to Quantum-Classical Reduction. [Published Article]

Hawking Effect as Quantum Inertial Effect. (arXiv:1510.06478v1 [hep-th])

on 2015-10-23 1:58am GMT

Authors: Yu-Lei Feng, Yi-Xin Chen

We show that “particle production” by gravitational field, especially the Hawking effect, may be treated as some quantum inertial effect, with the energy of Hawking radiation as some vacuum energy shift. This quantum inertial effect is mainly resulted from some intrinsical energy fluctuation $\hbar\kappa/c$ for a black hole. In particular, there is an extreme case in which $\hbar\kappa/c$ is the Planck energy, giving a “Planck black hole” whose event horizon’s diameter is one Planck length. Moreover, we also provide a possibility to obtain some positive cosmological constant for an expanding universe, which is induced from the vacuum energy shift caused by quantum inertial effect.

on 2015-10-23 1:58am GMT

Authors: Marco Túlio Quintino, Joseph Bowles, Flavien Hirsch, Nicolas Brunner

The observation of quantum nonlocality, i.e. quantum correlations violating a Bell inequality, implies the use of incompatible local quantum measurements. Here we consider the converse question. That is, can any set of incompatible measurements be used in order to demonstrate Bell inequality violation? Our main result is to construct a local hidden variable model for an incompatible set of qubit measurements. Specifically, we show that if Alice uses this set of measurements, then for any possible shared entangled state, and any possible projective measurements performed by Bob, the resulting statistics are local. This represents significant progress towards proving that measurement incompatibility does not imply Bell nonlocality in general.

A live alternative to quantum spooks. (arXiv:1510.06712v1 [quant-ph])

on 2015-10-23 1:58am GMT

Authors: Huw Price, Ken Wharton

Quantum weirdness has been in the news recently, thanks to an ingenious new experiment by a team led by Roland Hanson, at the Delft University of Technology. Much of the coverage presents the experiment as good (even conclusive) news for spooky action-at-a-distance, and bad news for local realism. We point out that this interpretation ignores an alternative, namely that the quantum world is retrocausal. We conjecture that this loophole is missed because it is confused for superdeterminism on one side, or action-at-a-distance itself on the other. We explain why it is different from these options, and why it has clear advantages, in both cases.

on 2015-10-23 1:58am GMT

Authors: Jing-Ling Chen, Xiang-Jun Ye

Quantum nonlocality has recently been classified into three distinct types: quantum entanglement, Einstein-Podolsky-Rosen (EPR) steering, and Bell’s nonlocality. Experimentally Bell’s nonlocality is usually tested by quantum violation of the Clause-Horne-Shimony-Holt (CHSH) inequality in the two-qubit system. Bell’s nonlocality is the strongest type of nonlocality, also due this reason Bell-test experiments have encountered both the locality loophole and the detection loophole for a very long time. As a weaker nonlocality, EPR steering naturally escapes from the locality loophole and is correspondingly easier to be demonstrated without the detection loophole. In this work, we trigger an extraordinary approach to investigate Bell’s nonlocality, which is strongly based on the EPR steering. We present a theorem, showing that for any two-qubit state $\tau$, if its mapped state $\rho$ is EPR steerable, then the state $\tau$ must be Bell nonlocal. The result not only pinpoints a deep connection between EPR steering and Bell’s nonlocality, but also sheds a new light to realize a loophole-free Bell-test experiment (without the CHSH inequality) through the violation of steering inequality.

on 2015-10-23 1:58am GMT

Authors: Maaneli Derakhshani

Wallstrom’s criticism of existing formulations of stochastic mechanics is that they fail to derive quantum theory because they require an \emph{ad hoc} quantization condition on the postulated velocity potential, \emph{S}, in order to derive single-valued Schr\”odinger wave functions. We propose an answer to this criticism by modifying the Nelson-Yasue formulation of non-relativistic stochastic mechanics for spinless particles with the following hypothesis: a spinless Nelson-Yasue particle of rest mass \emph{m} always undergoes simple harmonic `zitterbewegung’ (\emph{zbw}) oscillations in its instantaneous mean rest frame. With this hypothesis we show that, in the mean lab frame, \emph{S} arises as the mean \emph{zbw} phase for an ensemble of such particles, satisfies the required quantization condition, and evolves by the Nelson-Yasue stochastic equations of motion (which are thereby equivalent to the Schr\”odinger equation). The paper begins by reviewing Nelson-Yasue stochastic mechanics and Wallstrom’s criticism, after which we develop a classical model of a particle of mass \emph{m} undergoing the hypothesized \emph{zbw} oscillations, with the purpose of making clear the physical assumptions of the \emph{zbw} model without the added complications of stochastic mechanics. We develop the classical model for the spinless one-particle case, without and with field interactions, and then carry out the analogous developments for a Nelson-Yasue version of this model. Using this `zitterbewegung stochastic mechanics’ (ZSM) we readily derive the single-valued wave functions of non-relativistic quantum mechanics for a spinless particle in the analyzed cases. We also apply ZSM to the case of a central potential and show that it predicts angular momentum quantization.

A Separable, Dynamically Local Ontological Model of Quantum Mechanics

Latest Results for Foundations of Physics

on 2015-10-23 12:00am GMT

**Abstract**

A model of reality is called separable if the state of a composite system is equal to the union of the states of its parts, located in different regions of space. Spekkens has argued that it is trivial to reproduce the predictions of quantum mechanics using a separable ontological model, provided one allows for arbitrary violations of ‘dynamical locality’. However, since dynamical locality is strictly weaker than local causality, this leaves open the question of whether an ontological model for quantum mechanics can be both separable and dynamically local. We answer this question in the affirmative, using an ontological model based on previous work by Deutsch and Hayden. Although the original formulation of the model avoids Bell’s theorem by denying that measurements result in single, definite outcomes, we show that the model can alternatively be cast in the framework of ontological models, where Bell’s theorem does apply. We find that the resulting model violates local causality, but satisfies both separability and dynamical locality, making it a candidate for the ‘most local’ ontological model of quantum mechanics.

[Perspective] Chiral anomaly without relativity

on 2015-10-23 12:00am GMT

The Dirac equation, which describes relativistic fermions (like electrons moving at nearly the speed of light), has a mathematically inevitable but puzzling feature: negative-energy solutions. The physical reality of these solutions is unquestionable, as one of their direct consequences—the existence of antimatter—is confirmed by experiment. However, the interpretation of the solutions has always been somewhat controversial. Dirac’s own idea was to view the vacuum as a state in which all the negative energy levels are physically filled. This “Dirac sea” idea seems to contradict a common-sense view of the vacuum as a state in which matter is absent. On the other hand, the Dirac sea is a very natural concept from the point of view of condensed matter physics, as there is a direct and simple analogy: filled valence bands of an insulating crystal. There exists, however, a phenomenon within the context of relativistic quantum field theory, whose satisfactory understanding seems to be hard to achieve without assigning physical reality to the Dirac sea. This phenomenon, the chiral anomaly, presents a quantum mechanical violation of chiral symmetry; it was first observed experimentally in particle physics as a decay of a neutral pion into two photons. On page 413 of this issue, Xiong et al. (1) report the observation of this phenomenon in a condensed matter system—a crystal of Na3Bi—manifesting as an unusual negative longitudinal magnetoresistance; the vacuum/insulating crystal analogy is now all the more tangible. Author: Anton Burkov

Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres

Nature Physical Sciences Research

on 2015-10-21 12:00am GMT

More than 50 years ago, John Bell proved that no theory of nature that obeys locality and realism can reproduce all the predictions of quantum theory: in any local-realist theory, the correlations between outcomes of measurements on distant particles satisfy an inequality that can be violated if the particles are entangled. Numerous Bell inequality tests have been reported; however, all experiments reported so far required additional assumptions to obtain a contradiction with local realism, resulting in ‘loopholes’. Here we report a Bell experiment that is free of any such additional assumption and thus directly tests the principles underlying Bell’s inequality. We use an event-ready scheme that enables the generation of robust entanglement between distant electron spins (estimated state fidelity of 0.92 ± 0.03). Efficient spin read-out avoids the fair-sampling assumption (detection loophole), while the use of fast random-basis selection and spin read-out combined with a spatial separation of 1.3 kilometres ensure the required locality conditions. We performed 245 trials that tested the CHSH–Bell inequality S ≤ 2 and found S = 2.42 ± 0.20 (where S quantifies the correlation between measurement outcomes). A null-hypothesis test yields a probability of at most P = 0.039 that a local-realist model for space-like separated sites could produce data with a violation at least as large as we observe, even when allowing for memory in the devices. Our data hence imply statistically significant rejection of the local-realist null hypothesis. This conclusion may be further consolidated in future experiments; for instance, reaching a value of P = 0.001 would require approximately 700 trials for an observed S = 2.4. With improvements, our experiment could be used for testing less-conventional theories, and for implementing device-independent quantum-secure communication and randomness certification.

Nature doi: 10.1038/nature15759

Quantum physics: Death by experiment for local realism

Nature Physical Sciences Research

on 2015-10-21 12:00am GMT

A fundamental scientific assumption called local realism conflicts with certain predictions of quantum mechanics. Those predictions have now been verified, with none of the loopholes that have compromised earlier tests.

Nature doi: 10.1038/nature15631

Quantum cognition and bounded rationality

on 2015-10-20 12:00am GMT

**Abstract**

We consider several puzzles of bounded rationality. These include the Allais- and Ellsberg paradox, the disjunction effect, and related puzzles. We argue that the present account of quantum cognition—taking quantum probabilities rather than classical probabilities—can give a more systematic description of these puzzles than the alternate treatments in the traditional frameworks of bounded rationality. Unfortunately, the quantum probabilistic treatment does not always provide a deeper understanding and a true explanation of these puzzles. One reason is that quantum approaches introduce additional parameters which possibly can be *fitted* to empirical data but which do not necessarily *explain *them. Hence, the phenomenological research has to be augmented by responding to deeper foundational issues. In this article, we make the general distinction between foundational and phenomenological research programs, explaining the foundational issue of quantum cognition from the perspective of operational realism. This framework is motivated by assuming *partial* Boolean algebras (describing particular perspectives). They are combined into a uniform system (i.e. orthomodular lattice) via a mechanism preventing the simultaneous realization of perspectives. Gleason’s theorem then automatically leads to a distinction between probabilities that are defined by pure states and probabilities arising from the statistical mixture of pure states. This formal distinction relates to the conceptual distinction between risk and ignorance. Another outcome identifies quantum aspects in dynamic macro-systems using the framework of *symbolic dynamics*. Finally, we discuss several ideas that are useful for justifying complementarity in cognitive systems.