# Weekly Papers on Quantum Foundations (46)

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.

Quantum mechanics as an approximated model: A geometrodynamical approach. (arXiv:1607.04958v3 [gr-qc] UPDATED)

on 2016-11-11 8:44am GMT

Authors: Tomer Shushi

In this paper we discuss on a geometrodynamical approach to particle physics, in which quantum mechanics is no more than approximated model of nature in the microscopic scale. We argue that quantum phenomena can be obtained from the stress-energy tensor of the particle. Furthermore, we introduce a novel formulation that describes any particle in nature using the sum of the kernel of the particle, which is a simple Pseudo-Riemannian metric, and a non-local metric, a metric that describes non-local behaviur of spacetime. We then derive quantum mechanics from the concept of non-local geometrodynamics. Using the concept of superoscillations we obtain the metric of the particles which allows to map this metric into the quantum wavefunction representation.

What do we learn from computer simulations of Bell experiments?. (arXiv:1611.03444v1 [quant-ph])

on 2016-11-11 1:45am GMT

Authors: Marian Kupczynski

Contrary to counterfactual definiteness quantum theory teaches us that measuring instruments are not passively reading predetermined values of physical observables. Counterfactual definiteness allows proving Bell inequalities. If the contextual character of quantum measurements is correctly taken into account the proofs of these inequalities may not be done. In recent computer simulations of idealized Bell experiment predetermined successive outcomes of measurements for each setting and predetermined time delays of their registrations are calculated. Time windows and time delays are used to select various samples. Correlations, estimated using these selected samples are consistent with the predictions of quantum theory and the time window dependence is similar to the dependence observed in some real experiments. It is an important example how correlations can be explained without evoking quantum magic. However by using a suitable post-selection one may prove anything. Moreover before the post-selection generated samples may not violate Bell inequalities as significantly as finite samples generated using quantum predictions therefore we disagree with the conclusion that counterfactual definiteness is not able to distinguish classical from quantum physics. Moreover we show that for each choice of a time window there exists a contextual hidden variable probabilistic model consistent with the post-selection procedure used by the authors what explains why they are able to reproduce quantum predictions.

Introduction to “Standing together in Troubled Times”. (arXiv:1611.03133v1 [physics.hist-ph])

on 2016-11-11 1:45am GMT

Authors: M. Shifman

This Introduction opens the book {\sl Standing Together in Troubled Times} which presents a story of friendship between Wolfgang Pauli, one of the greatest theoretical physicists of the 20th century, and Charlotte Houtermans. They met at the very onset of the quantum era, in the late 1920s in Germany where Charlotte was a physics student at G\”ottingen University. At that time G\”ottingen was right at the heart of groundbreaking developments in physics. Both Pauli and Houtermans personally knew major participants in the quantum revolution. Caught between two evils — German National Socialism and Soviet Communism — Charlotte Houtermans would have likely perished if it were not for the brotherhood of physicists: Niels Bohr, Wolfgang Pauli, Albert Einstein, James Franck, Max Born, Robert Oppenheimer and many other noted scientists who tried to save friends and colleagues (either leftist sympathizers or Jews) who were in mortal danger of becoming entrapped in a simmering pre-WWII Europe. This book is based on newly discovered documents from the Houtermans family archive, including Pauli’s numerous letters to Houtermans, her correspondence with other great physicists, her diaries, and interviews with her children. Almost all documents presented in this book are being published for the first time.

Vacuum Measurements and Quantum State Reconstruction of Phonons. (arXiv:1611.03209v1 [quant-ph])

on 2016-11-11 1:41am GMT

A quantum state is fully characterized by its density matrix or equivalently by its quasiprobabilities in phase space. A scheme to identify the quasiprobabilities of a quantum state is an important tool in the recent development of quantum technologies. Based on our highly efficient vacuum measurement scheme, we measure the quasiprobability $Q$-function of the vibrational motion for a \Yb ion {\it resonantly} interacting with its internal energy states. This interaction model is known as the Jaynes-Cummings model which is one of the fundamental models in quantum electrodynamics. We apply the capability of the vacuum measurement to study the Jaynes-Cummings dynamics, where the Gaussian peak of the initial coherent state is known to bifurcate and rotate around the origin of phase space. They merge at the so-called revival time at the other side of phase space. The measured $Q$-function agrees with the theoretical prediction. Moreover, we reconstruct the Wigner function by deconvoluting the $Q$-function and observe the quantum interference in the Wigner function at half of the revival time, where the vibrational state becomes nearly disentangled from the internal energy states and forms a superposition of two composite states. The scheme can be applied to other physical setups including cavity or circuit-QED and optomechanical systems.

Null weak values and the past of a quantum particle. (arXiv:1611.02780v1 [quant-ph])

on 2016-11-10 12:52pm GMT

Authors: Q. DupreyA. Matzkin

Non-destructive weak measurements (WM) made on a quantum particle allow to extract information as the particle evolves from a prepared state to a finally detected state. The physical meaning of this information has been open to debate, particularly in view of the apparent discontinuous trajectories of the particle recorded by WM. In this work we investigate the properties of vanishing weak values for projection operators as well as general observables. We then analyze the implications when inferring the past of a quantum particle. We provide a novel (non-optical) example for which apparent discontinuous trajectories are obtained by WM.\ Our approach is compared to previous results.

The Meaning of the Wave Function: In Search of the Ontology of Quantum Mechanics. (arXiv:1611.02738v1 [quant-ph])

on 2016-11-10 12:52pm GMT

Authors: Shan Gao

The meaning of the wave function has been a hot topic of debate since the early days of quantum mechanics. Recent years have witnessed a growing interest in this long-standing question. Is the wave function ontic, directly representing a state of reality, or epistemic, merely representing a state of (incomplete) knowledge, or something else? If the wave function is not ontic, then what, if any, is the underlying state of reality? If the wave function is indeed ontic, then exactly what physical state does it represent? In this book, I aim to make sense of the wave function in quantum mechanics and find the ontological content of the theory. The book can be divided into three parts. The first part addresses the question of the nature of the wave function (Chapters 1-5). After giving a comprehensive and critical review of the competing views of the wave function, I present a new argument for the ontic view in terms of protective measurements. In addition, I also analyze the origin of the wave function by deriving the free Schroedinger equation. The second part analyzes the ontological meaning of the wave function (Chapters 6, 7). I propose a new ontological interpretation of the wave function in terms of random discontinuous motion of particles, and give two main arguments supporting this interpretation. The third part investigates whether the suggested quantum ontology is complete in accounting for our definite experience and whether it needs to be revised in the relativistic domain (Chapters 8, 9).

Quantum teleportation and Grover’s algorithm without the wavefunction

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

on 2016-11-09 8:55pm GMT

Niestegge, Gerd (2016) Quantum teleportation and Grover’s algorithm without the wavefunction. [Preprint]

Anchoring Causal Connections in Physical Concepts

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

on 2016-11-09 8:53pm GMT

Poellinger, Roland and Hubert, Mario (2014) Anchoring Causal Connections in Physical Concepts. [Preprint]

The theory of the Double Solution: Dynamical issues in quantum systems in the semiclassical regime. (arXiv:1611.02340v1 [quant-ph])

on 2016-11-09 11:25am GMT

Authors: A. Matzkin

The “dynamical mismatch” observed in quantum systems in the semiclassical regime challenge the Pilot wave model. Indeed the dynamics and properties of such systems depend on the trajectories of the classically equivalent system, whereas the de Broglie-Bohm trajectories are generically non-classical.\ In this work we examine the situation for the model favoured by de Broglie, the theory of the Double Solution (DS). We will see that the original DS model applied to semiclassical systems is also prone to the dynamical mismatch.\ However we will argue that the DS theory can be modified in order to yield propagation of the singularity in accord with the underlying classical dynamics of semiclassical systems.

Quantum State Reduction. (arXiv:1611.02664v1 [quant-ph])

on 2016-11-09 11:24am GMT

Authors: Dorje C. BrodyLane P. Hughston

We propose an energy-driven stochastic master equation for the density matrix as a dynamical model for quantum state reduction. In contrast, most previous studies of state reduction have considered stochastic extensions of the Schr\”odinger equation, and have introduced the density matrix as the expectation of the random pure projection operator associated with the evolving state vector. After working out properties of the reduction process we construct a general solution to the energy-driven stochastic master equation. The solution is obtained by the use of nonlinear filtering theory and takes the form of a completely positive stochastic map.

Black Holes, Information Loss and the Measurement Problem

Latest Results for Foundations of Physics

on 2016-11-09 12:00am GMT

Abstract

The information loss paradox is often presented as an unavoidable consequence of well-established physics. However, in order for a genuine paradox to ensue, not-trivial assumptions about, e.g., quantum effects on spacetime, are necessary. In this work we will be explicit about these additional, speculative assumptions required. We will also sketch a map of the available routes to tackle the issue, highlighting the, often overlooked, commitments demanded of each alternative. Finally, we will display the strong link between black holes, the issue of information loss and the measurement problem.

Meaning = Information + Evolution

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

on 2016-11-08 8:28pm GMT

ROVELLI, Carlo (2016) Meaning = Information + Evolution. [Preprint]

From Geometry to Conceptual Relativity

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

on 2016-11-08 8:18pm GMT

Barrett, Thomas William and Halvorson, Hans (2016) From Geometry to Conceptual Relativity. [Preprint]

Smooth Horizonless Geometries Deep Inside the Black-Hole Regime

PRL Editors’ Suggestions

on 2016-11-08 3:00pm GMT

Author(s): Iosif Bena, Stefano Giusto, Emil J. Martinec, Rodolfo Russo, Masaki Shigemori, David Turton, and Nicholas P. Warner

A novel class of horizonless supersymmetric black holes in five dimensions and their dual field theory descriptions are constructed, offering a specific realization of how the information content in a black hole can be consistent with quantum mechanics.

[Phys. Rev. Lett. 117, 201601] Published Tue Nov 08, 2016

Randomness in Quantum Mechanics: Philosophy, Physics and Technology. (arXiv:1611.02176v1 [quant-ph])

on 2016-11-08 1:46pm GMT

This progress report covers recent developments in the area of quantum randomness, which is an extraordinarily interdisciplinary area that belongs not only to physics, but also to philosophy, mathematics, computer science, and technology. For this reason the article contains three parts that will be essentially devoted to different aspects of quantum randomness, and even directed, although not restricted, to various audiences: a philosophical part, a physical part, and a technological part. For these reasons the article is written on an elementary level, combining very elementary and non-technical descriptions with a concise review of more advanced results. In this way readers of various provenances will be able to gain while reading the article.

CPT Symmetry Without Hermiticity. (arXiv:1611.02100v1 [hep-th])

on 2016-11-08 4:55am GMT

Authors: Philip D. Mannheim

In the literature the $CPT$ theorem has only been established for Hamiltonians that are Hermitian. Here we extend the $CPT$ theorem to quantum field theories with non-Hermitian Hamiltonians. Our derivation is a quite minimal one as it requires only the time independent evolution of scalar products and invariance under complex Lorentz transformations. The first of these requirements does not force the Hamiltonian to be Hermitian. Rather, it forces its eigenvalues to either be real or to appear in complex conjugate pairs, forces the eigenvectors of such conjugate pairs to be conjugates of each other, and forces the Hamiltonian to admit of an antilinear symmetry. The latter requirement then forces this antilinear symmetry to be $CPT$, with Hermiticity of a Hamiltonian thus only being a sufficient condition for $CPT$ symmetry and not a necessary one. $CPT$ symmetry thus has primacy over Hermiticity, and it rather than Hermiticity should be taken as a guiding principle for constructing quantum theories. With conformal gravity being a non-Hermitian theory, our approach allows us to construct a positive, ghost-free norm for the theory, to thereby establish the unitarity of conformal gravity. Since our approach allows for complex energies and decays, our work justifies the use of the $CPT$ theorem in establishing the equality of the lifetimes of unstable particles that are charge conjugates of each other. In the quantum-mechanical limit where charge conjugation is separately conserved, the key results of the $PT$ symmetry program of Bender and collaborators are recovered.

When Canonical Quantization Fails, Here is How to Fix It. (arXiv:1611.02107v1 [quant-ph])

on 2016-11-08 4:55am GMT

Authors: John R. Klauder

Following Dirac, the rules of canonical quantization include classical and quantum contact transformations of classical and quantum phase space variables. While arbitrary classical canonical coordinate transformations exist that is not the case for some analogous quantum canonical coordinate transformations. This failure is due to the rigid connection of quantum variables arising by promoting the corresponding classical variable from a $c$-number to a $q$-number. A different relationship of $c$-numbers and $q$-numbers in the procedures of Enhanced Quantization shows the compatibility of all quantum operators with all classical canonical coordinate transformations.

Maximum nonlocality in the (3,2,2) scenario. (arXiv:1611.01699v1 [quant-ph])

on 2016-11-08 4:55am GMT

We identify the simplest combinations of entanglement and incompatibility giving the maximum quantum violation for each of the 46 classes of tight Bell inequalities for the (3,2,2) scenario, i.e., three parties, two measurements per party, and two outcomes per measurement. This allows us to classify the maximum quantum nonlocality according to the simplest resources needed to achieve it. We show that entanglement and incompatibility only produce maximum nonlocality when they are combined in specific ways. For each entanglement class there is, in most cases, just one incompatibility class leading to maximum nonlocality. We also identify two interesting cases. We show that the maximum quantum violation of \’Sliwa inequality 23 only occurs when the third party measures the identity, so nonlocality cannot increase when we add a third party to the bipartite case. Surprisingly, almost quantum correlations predict that adding a new party increases nonlocality. This points out that either almost quantum correlations violate a fundamental principle or that there is a form of tripartite entanglement which quantum theory cannot account. The other interesting case is the maximum quantum violation of \’Sliwa inequality 26, which, like Mermin inequality, requires maximum incompatibility for all parties. In contrast, it requires a specific entangled state which has the same tripartite negativity as the W state.

Entanglement from Topology in Chern-Simons Theory. (arXiv:1611.01516v1 [quant-ph])

on 2016-11-08 4:55am GMT

Authors: Grant SaltonBrian SwingleMichael Walter

The way in which geometry encodes entanglement is a topic of much recent interest in quantum many-body physics and the AdS/CFT duality. This relation is particularly pronounced in the case of topological quantum field theories, where topology alone determines the quantum states of the theory. In this work, we study the set of quantum states that can be prepared by the Euclidean path integral in three-dimensional Chern-Simons theory. Specifically, we consider arbitrary 3-manifolds with a fixed number of torus boundaries in both abelian U(1) and non-abelian SO(3) Chern-Simons theory. For the abelian theory, we find that the states that can be prepared coincide precisely with the set of stabilizer states from quantum information theory. This constrains the multipartite entanglement present in this theory, but it also reveals that stabilizer states can be described by topology. In particular, we find an explicit expression for the entanglement entropy of a many-torus subsystem using only a single replica, as well as a concrete formula for the number of GHZ states that can be distilled from a tripartite state prepared through path integration. For the nonabelian theory, we find a notion of “state universality”, namely that any state can be prepared to an arbitrarily good approximation. The manifolds we consider can also be viewed as toy models of multi-boundary wormholes in AdS/CFT.

Quantum Processes Which Do Not Use Coherence

Recent Articles in Phys. Rev. X

on 2016-11-07 3:00pm GMT

Author(s): Benjamin Yadin, Jiajun Ma, Davide Girolami, Mile Gu, and Vlatko Vedral

Coherence is a fundamental feature of quantum theory and promises to underpin many future quantum technologies. By studying processes where it is not a necessary resource, researchers sharpen the theory of coherence finding links with interferometry and quantum correlations.

[Phys. Rev. X 6, 041028] Published Mon Nov 07, 2016

What Are Observables in Hamiltonian Theories? Testing Definitions with Empirical Equivalence

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

on 2016-11-05 11:38pm GMT

Pitts, J. Brian (2016) What Are Observables in Hamiltonian Theories? Testing Definitions with Empirical Equivalence. In: UNSPECIFIED.

Gravity can significantly modify classical and quantum Poincare recurrence theorems. (arXiv:1611.00792v1 [gr-qc])

on 2016-11-05 8:00am GMT

Authors: Ruifeng DongDejan Stojkovic

Poincare recurrence theorem states that any finite system will come arbitrary close to its initial state after some very long but finite time. At the statistical level, this by itself does not represent a paradox, but apparently violates the second law of thermodynamics, which may lead to some confusing conclusions for macroscopic systems. However, this statement does not take gravity into account. If two particles with a given center of mass energy come at the distance shorter than the Schwarzschild diameter apart, according to classical gravity they will form a black hole. In the classical case, a black hole once formed will always grow and effectively quench the Poincare recurrence. We derive the condition under which the classical black hole production rate is higher than the classical Poincare recurrence rate. In the quantum case, if the temperature of the black hole is lower than the temperature of the surrounding gas, such a black hole cannot disappear via Hawking evaporation. We derive the condition which gives us a critical temperature above which the black hole production is faster than quantum Poincare recurrence time. However, in quantum case, the quantum Poincare recurrence theorem can be applied to the black hole states too. The presence of the black hole can make the recurrence time longer or shorter, depending on whether the presence of the black hole increases or decreases the total entropy. We derive the temperature below which the produced black hole increases the entropy of the whole system (gas particles plus a black hole). Finally, if evolution of the system is fast enough, then newly formed black holes will merge and accrete particles until one large black hole dominates the system. We give the temperature above which the presence of black holes increase the entropy of the whole system and prolongs the Poincare recurrence time.