Weekly Papers on Quantum Foundations (51+)

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.

Against free will in the contemporary natural sciences

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

on 2016-12-24 5:33am GMT

López-Corredoira, Martín (2016) Against free will in the contemporary natural sciences. [Published Article or Volume]

Lewis, Peter J. (2016) Quantum mechanics, emergence, and fundamentality. [Preprint]

Authors: Santiago CodesidoMarcos Marino

We show that the all-orders WKB periods of one-dimensional quantum mechanical oscillators are governed by the refined holomorphic anomaly equations of topological string theory. We analyze in detail the double-well potential and the cubic and quartic oscillators. We calculate their quantum free energies to high order in the WKB expansion by using the direct integration of the anomaly equations. We reproduce in this way all known results about the quantum periods of these models, which we express in terms of modular forms on the WKB curve. As an application of our results, we study the large order behavior of the WKB expansion in the case of the double well, which displays the double factorial growth typical of string theory.

Authors: Paolo GloriosoHong Liu

The second law of thermodynamics states that for a thermally isolated system entropy never decreases. Most physical processes we observe in nature involve variations of macroscopic quantities over spatial and temporal scales much larger than microscopic molecular collision scales and thus can be considered as in local equilibrium. For a many-body system in local equilibrium a stronger version of the second law applies which says that the entropy production at each spacetime point should be non-negative. In this paper we provide a first derivation of this local second law of thermodynamics. For this purpose we develop a general non-equilibrium effective field theory of slow degrees of freedom from integrating out fast degrees of freedom in a quantum many-body system and consider its classical limit. The key elements of the proof are the presence of a $Z_2$ symmetry, which can be considered a non-equilibrium generalization of detailed balance condition, and a classical remnant of quantum unitarity. The $Z_2$ symmetry leads to a local current from a procedure analogous to that used in the Noether theorem. Unitarity leads to a definite sign of the divergence of the current. We also discuss the origin of an arrow of time, as well as the coincidence of causal and thermodynamical arrows of time. Applied to hydrodynamics, the proof gives a first-principle derivation of the phenomenological entropy current condition and provides a constructive procedure for obtaining the entropy current.

Authors: Slava Emelyanov

One might expect far away from physical black holes that quantum field quantisation performed in Minkowski space is a good approximation. Indeed, all experimental tests in particle colliders reveal no deviations so far. Nevertheless, the black holes should leave certain imprints of their presence in quantum processes. In this paper, we shall discuss several local imprints of small, primordial evaporating black holes in quantum electrodynamics in the weak gravity regime. Physically this can be interpreted as being macroscopic manifestations of vacuum fluctuations.

Authors: A. Yu. Ignatiev

A long-standing quantum-mechanical puzzle is whether the collapse of the wave function is a real physical process or simply an epiphenomenon. This puzzle lies at the heart of the measurement problem. One way to choose between the alternatives is to assume that one or the other is correct and attempt to draw physical, observable consequences which then could be empirically verified or ruled out. As a working hypothesis, we propose simple models of collapse as a real physical process for direct binary symmetric measurements made on one particle. This allows one to construct irreversible unstable Schr\”odinger equations capable of describing continuously the process of collapse induced by the interaction of the quantum system with the measuring device. Due to unknown initial conditions the collapse outcome remains unpredictable so no contradictions with quantum mechanics arise. Our theoretical framework predicts a finite time-scale of the collapse and links with experiment. Sensitive probes of the collapse dynamics could be done using Bose-Einstein condensates, ultracold neutrons or ultrafast optics. If confirmed, the formulation could be relevant to the transition from quantum fluctuations to classical inhomogeneities in early cosmology and to establishing the ultimate limits on the speed of quantum computation and information processing.

Authors: Gilles Cohen-Tannoudji

The vanishing of the spatial curvature observed in the current standard model of cosmology is interpreted under the assumption that it does not result from an accidental compensation mechanism between the contributions of visible matter and an unknown component called dark matter, but rather from a foundational principle relating matter to the vacuum, the principle of the relativity of inertia, or Mach’s principle. The dark universe (dark energy and dark matter) is thus interpreted as emerging together with ordinary matter, from the vacuum, as it is understood in the framework of quantum field theory, namely a quantum vacuum. It will be shown that this interpretation may lead to a reasonable agreement between the current understanding of the quantum vacuum in quantum field theory and current observations of dark energy and dark matter, and that dark matter can be interpreted as emerging from the QCD vacuum, as a Bose-Einstein gluon condensate, with an energy density relative to the baryonic energy density that agrees with observations.

Authors: Natacha AltamiranoPaulina Corona-UgaldeRobert B. MannMagdalena Zych

It is currently believed that we have no experimental evidence on gravity-inspired modifications to quantum mechanics, such as the Diosi-Penrose model. Furthermore, it is widely accepted that the most auspicious approach to verifying such models are quantum tests with large massive systems, realized with optomechanical or large-molecule interferometric setups. Here we show that single-atom interference experiments achieving large spatial superpositions rule out the gravitational decoherence model of Kafri, Taylor and Milburn. Experiments thus show that gravitational interactions cannot be described as pairwise local classical channels between massive particles. We discuss how the same experiments impose constraints on other related models.

Authors: Luigi SevesoMatteo G. A. Paris

We address the question whether, as a matter of principle, a quantum probe in a gravitational field may be considered as a test particle obeying the weak equivalence principle (WEP). To this aim we put forward a quantitative generalization of the WEP, which applies also to quantum systems, while maintaining the physical content of its classical formulation. Our formulation of the WEP is information-theoretic in nature, and requires that information about the mass of a probe, as obtained from position measurements, cannot increase in the presence of a gravitational field. More precisely, the generalized WEP states that the Fisher information of position measurements cannot increase in the presence of gravity, compared to its value for a free probe. Our results show that while in a uniform field quantum probes satisfy the WEP exactly, gravity gradients may encode nontrivial information about the mass in the particle’s wavefunction, thus leading to violations of the WEP. We conclude that the WEP is untenable for a quantum particle described by a wavefunction, which rather behaves in analogy with a classical extended object.

Authors: Natacha AltamiranoPaulina Corona-UgaldeRobert B. MannMagdalena Zych

It is currently believed that we have no experimental evidence on gravity-inspired modifications to quantum mechanics, such as the Diosi-Penrose model. Furthermore, it is widely accepted that the most auspicious approach to verifying such models are quantum tests with large massive systems, realized with optomechanical or large-molecule interferometric setups. Here we show that single-atom interference experiments achieving large spatial superpositions rule out the gravitational decoherence model of Kafri, Taylor and Milburn. Experiments thus show that gravitational interactions cannot be described as pairwise local classical channels between massive particles. We discuss how the same experiments impose constraints on other related models.

Authors: Marco BilardelloAndrea TrombettoniAngelo Bassi

We investigate how ultracold atoms in double well potentials can be used to study and put bounds on models describing wave function collapse. We refer in particular to the continuous spontaneous localization (CSL) model, which is the most well studied among dynamical reduction models. It modifies the Schrodinger equation in order to include the collapse of the wave function in its dynamics. We consider Bose Josephson junctions, where ultracold bosons are trapped in a double well potential,since they can be experimentally controlled with high accuracy and are suited and used to study macroscopic quantum phenomena on scale of microns with a number of particles typically ranging from $\sim 10^2-10^3$ to $\sim 10^5-10^6$. We study the CSL dynamics of three atomic states showing macroscopic quantum coherence: the atomic coherent state, the superposition of two atomic coherent states, and the NOON state. We show that for the last two states the suppression of quantum coherence induced by CSL model increases exponentially with the number of atoms. We observe that, in the case of optically trapped atoms, the spontaneous photon emission of the atoms induce a dynamics similar to the CSL one and we conclude that magnetically trapped atoms may be more convenient to experimentally test the CSL model. We finally discuss decoherence effects in order to provide reasonable estimates on the bounds that it is (or it will) possible to obtain for the parameters of the CSL model in such class of experiments: as an example, we show that a NOON state with $N \sim 10^3$ with a coherence time of $\sim 1$ s can constrain the CSL parameters in a region where the other systems presently cannot.

Publication date: Available online 22 December 2016
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Darren Bradley
David Deutsch (forthcoming) offers a solution to the Epistemic Problem for Everettian Quantum Theory. In this note I raise some problems for the attempted solution.

Quantum Leaps in the Wrong Direction

 Physics

on 2016-12-23 12:00am GMT

Author: Charles M. Wynn, Arthur W. Wiggins, and Illustrated by Sidney Harris
ISBN: 9780190620295
Binding: Hardcover
Publication Date: 23 December 2016
Price: $35.00

Authors: Laura Mersini-Houghton

The 2015 Planck data release has placed tight constraints on the class of in ationary models allowed. The current best fit region favors concave downwards in ationary potentials, since they produce a suppressed tensor to scalar index ratio r. Concave downward potentials have a negative curvature V”<0, therefore a tachyonic mass square that drives fluctuations. Furthermore, their use can become problematic if the field rolls in a part of the potential away from the extrema, since the semiclassical approximation of quantum cosmology, used for deriving the most probable wavefunction of the universe from the landscape and for addressing the quantum to classical transition, breaks down away from the steepest descent region. We here propose a way of dealing with such potentials by inverting the metric signature and solving for the wavefunction of the universe in the Euclidean sector. This method allows us to extend our theory of the origin of the universe from a quantum multiverse, to a more general class of concave inflationary potentials where a straightforward application of the semiclassical approximation fails. The work here completes the derivation of modifications to the Newtonian potential and to the inflationary potential, which originate from the quantum entanglement of our universe with all others in the quantum landscape multiverse, leading to predictions of observational signatures for both types of in ationary models, concave and convex potentials.

Authors: Christopher A. FuchsBlake C. Stacey

This paper represents an elaboration of the lectures delivered by one of us (CAF) during “Course 197 — Foundations of Quantum Physics” at the International School of Physics “Enrico Fermi” in Varenna, Italy, July 2016. Much of the material for it is drawn fromarXiv:1003.5209arXiv:1401.7254, and arXiv:1405.2390. However there are substantial additions of original material in Sections 4, 7, 8 and 9, along with clarifications and expansions of the older content throughout. Topics include the meaning of subjective probability; no-cloning, teleportation, and quantum tomography from the subjectivist Bayesian perspective; the message QBism receives from Bell inequality violations (namely, that nature is creative); the import of symmetric informationally complete (SIC) quantum measurements for the technical side of QBism; quantum cosmology QBist-style; and a potential meaning for the holographic principle within QBism.

Authors: Yuta MichimuraYuya KuwaharaTakafumi UshibaNobuyuki MatsumotoMasaki Ando

We propose a new method to optically levitate a macroscopic mirror with two vertical Fabry-P{\’e}rot cavities linearly aligned. This configuration gives the simplest possible optical levitation in which the number of laser beams used is the minimum of two. We demonstrate that reaching the standard quantum limit (SQL) of a displacement measurement with our system is feasible with current technology. The cavity geometry and the levitated mirror parameters are designed to ensure that the Brownian vibration of the mirror surface is smaller than the SQL. Our scheme provides a promising tool for various tests of macroscopic quantum mechanics.

Authors: Ravi Kunjwal

When it isn’t possible to tell two distinct experimental procedures apart purely from their input/output statistics, then it seems a plausible hypothesis that the two procedures must be physically identical. We call such a hypothesis “noncontextuality”, an instance of Leibniz’s principle of the identity of indiscernibles. Read in the contrapositive, this hypothesis entails that any physical distinctions between two experimental procedures must necessarily lead to a difference in their operational statistics. The results I present in this thesis concern the failure of this hypothesis — a failure dubbed “contextuality” — when one tries to embed an operational theory (such as quantum theory) in the ontological models framework. The Kochen-Specker theorem demonstrates the failure of noncontextuality for deterministic ontological models of quantum theory, i.e., those ontological models where the ontic/physical state of the system fixes the outcome of any projective measurement on the system in a deterministic manner. This thesis goes beyond the Kochen-Specker (KS) theorem by asking what operational facts must be verified in experiments to conclude that Nature does not admit noncontextual ontological models, not even indeterministic ones. This leads to noncontextuality inequalities that are robust to noise in the preparations and measurements. In the particular case of quantum theory, these inequalities are meaningful even when unsharp measurements (or POVMs) are allowed, a feature not shared by the traditional approach to KS-noncontextuality where unsharp measurements are excluded by fiat: allowing them renders even trivial POVMs (proportional to identity) maximally KS-contextual. The sense in which trivial POVMs are indeed “trivial” (or “noncontextual”) is clear in our approach: they are simply too noisy to lead to violation of our noncontextuality inequalities.

Authors: Lino ReggianiEleonora Alfinito

The role played by zero-point contribution, also called quantum noise or vacuum fluctuations, in the quantum expression of the fluctuation-dissipation theorem (FDT) is a long-standing open problem widely discussed by the physicist community since its announcement by Callen and Welton pioneer paper of 1951 [1]. From one hand, it has the drawbacks of: (i) the expectation value of its energy is infinite, (ii) it produces an ultraviolet catastrophe of the noise power spectral density and, (iii) it lacks of an experimental validation under thermal equilibrium conditions. From another hand, by imposing appropriate boundary conditions and eliminating divergences by regulation techniques, vacuum fluctuations are the source of an attractive force between opposite conducting plates, firstly predicted by Casimir in 1948 [2] and later validated experimentally with increasing accuracy. As a consequence, a quantum formulation of FDT should account for the presence of the Casimir force and of its consequences. In this letter we show that at thermal equilibrium the Casimir force should be balanced by the mechanical reaction of the physical system. As a consequence, no zero-point spectrum can be detected and the power spectrum emitted by the physical system is the same of that calculated by Planck in 1901 [3] for a black-body. Accordingly, the experimental validation of the standard expression of the quantum FDT [1] is prevented in favor of the Nyquist expression that includes the Planck factor [4].

Hoehn, Philipp A (2016) Quantum theory from rules on information acquisition. In: UNSPECIFIED.

Quantum spin liquids are exotic states of matter first predicted more than 40 years ago. An inorganic material has properties consistent with these predictions, revealing details about the nature of quantum matter. See Letter p.559

Nature 540 534 doi: 10.1038/540534a

Tang, Xianyi and Zhang, Zhilin (2016) A translation of “A New Solution to the Measurement Problem of Quantum Mechanics” by Xianyi Tang and Zhilin Zhang. Studies in Dialectics of Nature, Beijing, China.

Observation of Weak Collapse in a Bose-Einstein Condensate

 Recent Articles in Phys. Rev. X

on 2016-12-19 3:00pm GMT

Author(s): Christoph Eigen, Alexander L. Gaunt, Aziza Suleymanzade, Nir Navon, Zoran Hadzibabic, and Robert P. Smith

Researchers investigate a nonlinear wave collapse phenomenon that has hitherto evaded experimental detection.

[Phys. Rev. X 6, 041058] Published Mon Dec 19, 2016

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