# Weekly Papers on Quantum Foundations (5)

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

Short-time quantum propagator and Bohmian trajectories

ScienceDirect Publication: Physics Letters A

on 2015-1-30 10:33pm GMT

Publication date: 6 December 2013
Source:Physics Letters A, Volume 377, Issue 42
Author(s): Maurice de Gosson , Basil Hiley
We begin by giving correct expressions for the short-time action following the work Makri–Miller. We use these estimates to derive an accurate expression modulo Δ t 2 for the quantum propagator and we show that the quantum potential is negligible modulo Δ t 2 for a point source, thus justifying an unfortunately largely ignored observation of Holland made twenty years ago. We finally prove that this implies that the quantum motion is classical for very short times.

Necessary and sufficient conditions for macroscopic realism from quantum mechanics. (arXiv:1501.07517v1 [quant-ph])

on 2015-1-30 2:09am GMT

Authors: Lucas ClementeJohannes Kofler

Macroscopic realism, the classical world view that macroscopic objects exist independently of and are not influenced by measurements, is usually tested using Leggett-Garg inequalities. Recently, another necessary condition called no-signaling in time (NSIT) has been proposed as a witness for non-classical behavior. In this paper, we show that a combination of NSIT conditions is not only necessary but also sufficient for macroscopic realism. Any violation of macroscopic realism must therefore be witnessed by a suitable NSIT condition. Subsequently, we derive an operational formulation for NSIT in terms of positive-operator valued measurements and the system Hamiltonian. We argue that this leads to a suitable definition of “classical” measurements and Hamiltonians, and apply our formalism to some generic coarse-grained quantum measurements.

The Cofounder of Quantum Field Theory: Pascual Jordan. (arXiv:1501.07384v1 [physics.hist-ph])

on 2015-1-30 2:09am GMT

Authors: Walter Dittrich

A comparative study is undertaken that brings to light the two different methods of how to treat the many-body problem in quantum field theory. The two main researchers who published the first versions of how to quantize a many-body assembly were P. Jordan and P.A.M. Dirac. What they understood by the so-called “second quantization” will be the subject of the paper. We will argue that it is Jordan’s field operator approach that until now constitutes the basis of any work in quantum field theory.

Chunk and permeate II: Bohr’s hydrogen atom

Latest Results for European Journal for Philosophy of Science

on 2015-1-30 12:00am GMT

Abstract

Niels Bohr’s model of the hydrogen atom is widely cited as an example of an inconsistent scientific theory because of its reliance on classical electrodynamics (CED) together with assumptions about interactions between matter and electromagnetic radiation that could not be reconciled with CED. This view of Bohr’s model is controversial, but we believe a recently proposed approach to reasoning with inconsistent commitments offers a promising formal reading of how Bohr’s model worked. In this paper we present this new way of reasoning with inconsistent commitments and compare it with other approaches before applying it to Bohr’s model and offering some suggestions for how it might be extended to account for subsequent developments in old quantum theory (OQT).

Experimental test of environment-assisted invariance

PRA: Fundamental concepts

on 2015-1-29 3:00pm GMT

Author(s): L. Vermeyden, X. Ma, J. Lavoie, M. Bonsma, U. Sinha, R. Laflamme, and K. J. Resch

Envariance, or environment-assisted invariance, is a recently identified symmetry for maximally entangled states in quantum theory with important ramifications for quantum measurement, specifically for understanding Born’s rule. We benchmark the degree to which nature respects this symmetry by using…

[Phys. Rev. A 91, 012120] Published Thu Jan 29, 2015

Precision measurement: Relativity tested with a split electron

Nature Physical Sciences Research

on 2015-1-28 12:00am GMT

Splitting and recombining an electron wave packet has been used to test relativity at a record sensitivity. The result heralds an era of precision measurements of relativity using quantum-information methods. See Letter p.592

Nature 517 559 doi: 10.1038/517559a

Michelson–Morley analogue for electrons using trapped ions to test Lorentz symmetry

Nature Physical Sciences Research

on 2015-1-28 12:00am GMT

All evidence so far suggests that the absolute spatial orientation of an experiment never affects its outcome. This is reflected in the standard model of particle physics by requiring all particles and fields to be invariant under Lorentz transformations. The best-known tests of this important cornerstone of physics are Michelson–Morley-type experiments verifying the isotropy of the speed of light. For matter, Hughes–Drever-type experiments test whether the kinetic energy of particles is independent of the direction of their velocity, that is, whether their dispersion relations are isotropic. To provide more guidance for physics beyond the standard model, refined experimental verifications of Lorentz symmetry are desirable. Here we search for violation of Lorentz symmetry for electrons by performing an electronic analogue of a Michelson–Morley experiment. We split an electron wave packet bound inside a calcium ion into two parts with different orientations and recombine them after a time evolution of 95 milliseconds. As the Earth rotates, the absolute spatial orientation of the two parts of the wave packet changes, and anisotropies in the electron dispersion will modify the phase of the interference signal. To remove noise, we prepare a pair of calcium ions in a superposition of two decoherence-free states, thereby rejecting magnetic field fluctuations common to both ions. After a 23-hour measurement, we find a limit of h × 11 millihertz (h is Planck’s constant) on the energy variations, verifying the isotropy of the electron’s dispersion relation at the level of one part in 1018, a 100-fold improvement on previous work. Alternatively, we can interpret our result as testing the rotational invariance of the Coulomb potential. Assuming that Lorentz symmetry holds for electrons and that the photon dispersion relation governs the Coulomb force, we obtain a fivefold-improved limit on anisotropies in the speed of light. Our result probes Lorentz symmetry violation at levels comparable to the ratio between the electroweak and Planck energy scales. Our experiment demonstrates the potential of quantum information techniques in the search for physics beyond the standard model.

Nature 517 592 doi: 10.1038/nature14091

Quantum Superpositions Cannot be Epistemic. (arXiv:1501.05969v1 [quant-ph])

on 2015-1-27 1:56am GMT

Authors: John-Mark A. Allen

Quantum superposition states are behind many of the curious phenomena exhibited by quantum systems, including Bell non-locality, quantum interference, quantum computational speed-up, and the measurement problem. However, many qualitative properties of quantum superpositions can also be observed in classical probability distributions leading to a suspicion that superpositions may be explicable as probability distributions over less problematic states; that is, a suspicion that superpositions are \emph{epistemic}. Here, it is proved that, for any quantum system of dimension $d>3$, this cannot be the case for almost all superpositions. Equivalently, any underlying ontology must contain ontic superposition states. A related question concerns general possibility of non-orthogonal quantum states $|\psi\rangle,|\phi\rangle$ being ontologically indistinct. A similar method proves that if $|\langle\phi|\psi\rangle|^{2}\in(0,\frac{1}{4})$ then $|\psi\rangle,|\phi\rangle$ must approach ontological distinctness as $d\rightarrow\infty$. The robustness of these results to small experimental error is also discussed.

Dualities and Emergent Gravity: AdS/CFT and Verlinde’s Scheme. (arXiv:1501.06162v1 [physics.hist-ph])

on 2015-1-27 1:51am GMT

Authors: Sebastian de Haro

In this paper I analyse two closely related examples of duality and of emergence of gravity, namely AdS/CFT and Verlinde’s scheme. Based on the notion of duality introduced in Dieks et al. (2014), I here elaborate on the conditions necessary for AdS/CFT to be a duality, in particular the condition of completeness. I also address what is usually seen as a desideratum for any candidate theory of quantum gravity: the background-independence of the theory and the diffeomorphism invariance of the observables. Then I discuss Verlinde’s scheme and the extent to which it gives a clear case of emergence of gravity. Finally, I give a novel derivation of the Bekenstein-Hawking black hole entropy formula based on Verlinde’s scheme.

What is a wavefunction?

Latest Results for Synthese

on 2015-1-27 12:00am GMT

Abstract

Much of the the discussion of the metaphysics of quantum mechanics focusses on the status of wavefunctions. This paper is about how to think about wavefunctions, when we bear in mind that quantum mechanics—that is, the nonrelativistic quantum theory of systems of a fixed, finite number of degrees of freedom—is not a fundamental theory, but arises, in a certain approximation, valid in a limited regime, from a relativistic quantum field theory. We will explicitly show how the wavefunctions of quantum mechanics, and the configuration spaces on which they are defined, are constructed from a relativistic quantum field theory. Two lessons will be drawn from this. The first is that configuration spaces are not fundamental, but rather are derivative of structures defined on ordinary spacetime. The second is that wavefunctions are not as much like classical fields as might first appear, in that, on the most natural way of constructing wavefunctions from quantum field-theoretic quantities, the value assigned to a point in configuration space is not a local fact about that point, but rather, depends on the global state.

Non-classical conditional probability and the quantum no-cloning theorem

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

on 2015-1-25 3:48am GMT

Niestegge, Gerd (2015) Non-classical conditional probability and the quantum no-cloning theorem. In: [2015] Quantum computation, quantum information, and the exact sciences (Munich; 30-31 January 2015) .

Would the Existence of CTCs Allow for Nonlocal Signaling?

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

on 2015-1-25 3:44am GMT

Dunlap, Lucas (2015) Would the Existence of CTCs Allow for Nonlocal Signaling? In: [2015] Quantum computation, quantum information, and the exact sciences (Munich; 30-31 January 2015) .

Bell Inequality and Many-Worlds Interpretation

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

on 2015-1-25 3:42am GMT

Vaidman, Lev (2015) Bell Inequality and Many-Worlds Interpretation. [Preprint]