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.

The true quantum face of the “exponential” decay law. (arXiv:1606.07301v1 [quant-ph])

on 2016-6-25 8:04am GMT

Authors: K. Urbanowski

Results of theoretical studies of the quantum unstable systems caused that there are rather widespread belief that a universal feature od the quantum decay process is the presence of three time regimes of the decay process: the early time (initial) leading to the Quantum Zeno (or Anti Zeno) Effects, “exponential” (or “canonical”) described by the decay law of the exponential form, and late time characterized by the decay law having inverse–power law form. Based on the fundamental principles of the quantum theory we give the proof that there is no time interval in which the survival probability (decay law) could be a decreasing function of time of the purely exponential form but even at the “exponential” regime the decay curve is oscillatory modulated with a smaller or a large amplitude of oscillations depending on parameters of the model considered.

$\Psi$-Epistemic Quantum Cosmology?. (arXiv:1606.07265v1 [gr-qc])

on 2016-6-24 12:32pm GMT

Authors: Peter W. Evans, Sean Gryb, Karim P. Y. Thébault

This paper provides a prospectus for a new way of thinking about the wavefunction of the universe: a $\Psi$-epistemic quantum cosmology. We present a proposal that, if successfully implemented, would resolve the cosmological measurement problem and simultaneously allow us to think sensibly about probability and evolution in quantum cosmology. Our analysis draws upon recent work on the problem of time in quantum gravity, upon causally-symmetric local hidden variable theories, and upon a dynamical origin for the cosmological arrow of time. Our conclusion weighs the strengths and weaknesses of the approach and points towards paths for future development.

Non-Relativistic Limit of the Dirac Equation. (arXiv:1511.07901v3 [quant-ph] CROSS LISTED)

on 2016-6-23 7:32am GMT

Authors: Muhammad Adeel Ajaib

We show that the first order form of the Schrodinger equation proposed in [1] can be obtained from the Dirac equation in the non-relativistic limit. We also show that the Pauli Hamiltonian is obtained from this equation by requiring local gauge invariance. In addition, we study the problem of a spin up particle incident on a finite potential barrier and show that the known quantum mechanical results are obtained. Finally, we consider the symmetric potential well and show that the quantum mechanical expression for the quantized energy levels of a particle is obtained with periodic boundary conditions. Based on these conclusions, we propose that the equation introduced in [1] is the non-relativistic limit of the Dirac equation and more appropriately describes spin 1/2 particles in the non-relativistic limit.

on 2016-6-23 7:32am GMT

Authors: J. Brian Pitts

Classical and quantum field theory provide not only realistic examples of extant notions of empirical equivalence, but also new notions of empirical equivalence, both modal and occurrent. A simple but modern gravitational case goes back to the 1890s, but there has been apparently total neglect of the simplest relativistic analog, with the result that an erroneous claim has taken root that Special Relativity could not have accommodated gravity even if there were no bending of light. The fairly recent acceptance of nonzero neutrino masses shows that widely neglected possibilities for nonzero particle masses have sometimes been vindicated. In the electromagnetic case, there is permanent underdetermination at the classical and quantum levels between Maxwell’s theory and the one-parameter family of Proca’s electromagnetisms with massive photons, which approximate Maxwell’s theory in the limit of zero photon mass. While Yang-Mills theories display similar approximate equivalence classically, quantization typically breaks this equivalence. A possible exception, including unified electroweak theory, might permit a mass term for the photons but not the Yang-Mills vector bosons. Underdetermination between massive and massless (Einstein) gravity even at the classical level is subject to contemporary controversy.

Reflexive measurements, self-inspection and self-representation. (arXiv:1606.06938v1 [quant-ph])

physics.hist-ph updates on arXiv.org

on 2016-6-23 7:32am GMT

Authors: Karl Svozil

There exist limits of self-inspection due to self-referential paradoxes, incompleteness and fixed point theorems. As quantum mechanics dictates the exchange of discrete quanta, measurements and self-inspection of quantized systems are fundamentally limited.

Quantum Probability as an Application of Data Compression Principles. (arXiv:1606.06802v1 [cs.IT])

on 2016-6-23 5:06am GMT

Authors: Allan F. Randall

Realist, no-collapse interpretations of quantum mechanics, such as Everett’s, face the probability problem: how to justify the norm-squared (Born) rule from the wavefunction alone. While any basis-independent measure can only be norm-squared (due to the Gleason-Busch Theorem) this fact conflicts with various popular, non-wavefunction-based phenomenological measures – such as observer, outcome or world counting – that are frequently demanded of Everettians. These alternatives conflict, however, with the wavefunction realism upon which Everett’s approach rests, which seems to call for an objective, basis-independent measure based only on wavefunction amplitudes. The ability of quantum probabilities to destructively interfere with each other, however, makes it difficult to see how probabilities can be derived solely from amplitudes in an intuitively appealing way. I argue that the use of algorithmic probability can solve this problem, since the objective, single-case probability measure that wavefunction realism demands is exactly what algorithmic information theory was designed to provide. The result is an intuitive account of complex-valued amplitudes, as coefficients in an optimal lossy data compression, such that changes in algorithmic information content (entropy deltas) are associated with phenomenal transitions.

The Information Content of Systems in General Physical Theories. (arXiv:1606.06801v1 [cs.CC])

on 2016-6-23 5:06am GMT

Authors: Ciarán M. Lee (University of Oxford), Matty J. Hoban (University of Oxford)

What kind of object is a quantum state? Is it an object that encodes an exponentially growing amount of information (in the size of the system) or more akin to a probability distribution? It turns out that these questions are sensitive to what we do with the information. For example, Holevo’s bound tells us that n qubits only encode n bits of classical information but for certain communication complexity tasks there is an exponential separation between quantum and classical resources. Instead of just contrasting quantum and classical physics, we can place both within a broad landscape of physical theories and ask how non-quantum (and non-classical) theories are different from, or more powerful than quantum theory. For example, in communication complexity, certain (non-quantum) theories can trivialise all communication complexity tasks. In recent work [C. M. Lee and M. J. Hoban, Proc. Royal Soc. A 472 (2190), 2016], we showed that the immense power of the information content of states in general (non-quantum) physical theories is not limited to communication complexity. We showed that, in general physical theories, states can be taken as “advice” for computers in these theories and this advice allows the computers to easily solve any decision problem. Aaronson has highlighted the close connection between quantum communication complexity and quantum computations that take quantum advice, and our work gives further indications that this is a very general connection. In this work, we review the results in our previous work and discuss the intricate relationship between communication complexity and computers taking advice for general theories.

Lectures on the Quantum Hall Effect. (arXiv:1606.06687v1 [hep-th])

on 2016-6-22 9:42am GMT

Authors: David Tong

The purpose of these lectures is to describe the basic theoretical structures underlying the rich and beautiful physics of the quantum Hall effect. The focus is on the interplay between microscopic wavefunctions, long-distance effective Chern-Simons theories, and the modes which live on the boundary. The notes are aimed at graduate students in any discipline where $\hbar=1$. A working knowledge of quantum field theory is assumed. Contents:

1. The Basics (Landau levels and Berry phase).

2. The Integer Quantum Hall Effect.

3. The Fractional Quantum Hall Effect.

4. Non-Abelian Quantum Hall States.

5. Chern-Simons Theories.

6. Edge Modes.

The Puzzle of Empty Bottle in Quantum Theory. (arXiv:1606.06317v1 [quant-ph])

on 2016-6-22 8:01am GMT

Authors: Bogdan Mielnik

We discuss an extremely simple effect of ‘shadowing’ where the very existence of the measuring apparatus deforms the evolution of quantum states even if the measurement is never preformed. In spite of strange intuitive aspects, it might be related to some recent doubts about the completeness of quantum theories.

on 2016-6-22 8:01am GMT

Authors: Takuji Ishikawa

This study was started to know mysterious classicality of nuclei.

Using three particles model without external environments, it is found that decisions of respective state of three particles by decoherence are not simultaneous. Furthermore, in this model, wave function of total three body system collapses spontaneously without any external environments. Therefore we may able to insist that a wavefunction of our universe has already collapsed spontaneously without any external observer, because of the same mechanism with this model.

QBism and Quantum Nonlocality. (arXiv:1606.06286v1 [quant-ph])

on 2016-6-22 8:01am GMT

Authors: Gerold Gründler

The Quantum-Bayesian interpretation of quantum theory claims to eliminate the question of quantum nonlocality. This claim is not justified, because the question of non-locality does not arise due to any interpretation of quantum theory, but due to objective experimental facts.

on 2016-6-22 8:01am GMT

Authors: Alastair A. Abbott, Dominic C. Horsman

This volume constitutes the proceedings of the 7th International Workshop on Physics and Computation (PC 2016). The workshop was held on the 14th of July 2016 in Manchester, UK, as a satellite workshop to UCNC 2016, the 15th International Conference on Unconventional Computation and Natural Computation.

The goal of the workshop series is to bring together researches working on the interaction between physics and the theory of computation. This intrinsically interdisciplinary domain of research strives to go beyond the traditional use of mathematics as a tool to model and understand the behaviour of physical systems. Instead, it looks to the the theory of computation and information to provide new insights into physical systems and processes, and, in turn, how these insights can lead to new methods, models and notation of computation and new approaches to computational and mathematical problems. Topics falling into this category at the interface of physics and computation that are within the scope of the conference include, amongst many others, the axiomatisation of physics, hypercomputation, the role of information in physical systems, quantum information, randomness in physics, theories of measurement, and the philosophy of physics and computation.

Quantum computer makes first high-energy physics simulation

on 2016-6-22 12:00am GMT

The technique would help address problems that classical computers can’t handle.

Nature News doi: 10.1038/nature.2016.20136

Particle physics: Quantum simulation of fundamental physics

on 2016-6-22 12:00am GMT

Gauge theories underpin the standard model of particle physics, but are difficult to study using conventional computational methods. An experimental quantum system opens up fresh avenues of investigation. See Letter p.516

Nature 534 480 doi: 10.1038/534480a

Latest Results for Foundations of Physics

on 2016-6-22 12:00am GMT

**Abstract**

We introduce a new approach to analyzing the interaction between classical and quantum systems that is based on a limiting procedure applied to multi-particle Schrödinger equations. The limit equations obtained by this procedure, which we refer to as the classical-quantum limit, govern the interaction between classical and quantum systems, and they possess many desirable properties that are inherited in the limit from the multi-particle quantum system. As an application, we use the classical-quantum limit equations to identify the source of the non-local signalling that is known to occur in the classical-quantum hybrid scheme of Hall and Reginatto. We also derive the first order correction to the classical-quantum limit equation to obtain a fully consistent first order approximation to the Schrödinger equation that should be accurate for modeling the interaction between particles of disparate mass in the regime where the particles with the larger masses are effectively classical.

Real-time dynamics of lattice gauge theories with a few-qubit quantum computer

Nature Physical Sciences Research

on 2016-6-22 12:00am GMT

Gauge theories are fundamental to our understanding of interactions between the elementary constituents of matter as mediated by gauge bosons. However, computing the real-time dynamics in gauge theories is a notorious challenge for classical computational methods. This has recently stimulated theoretical effort, using Feynman’s idea of a quantum simulator, to devise schemes for simulating such theories on engineered quantum-mechanical devices, with the difficulty that gauge invariance and the associated local conservation laws (Gauss laws) need to be implemented. Here we report the experimental demonstration of a digital quantum simulation of a lattice gauge theory, by realizing (1 + 1)-dimensional quantum electrodynamics (the Schwinger model) on a few-qubit trapped-ion quantum computer. We are interested in the real-time evolution of the Schwinger mechanism, describing the instability of the bare vacuum due to quantum fluctuations, which manifests itself in the spontaneous creation of electron–positron pairs. To make efficient use of our quantum resources, we map the original problem to a spin model by eliminating the gauge fields in favour of exotic long-range interactions, which can be directly and efficiently implemented on an ion trap architecture. We explore the Schwinger mechanism of particle–antiparticle generation by monitoring the mass production and the vacuum persistence amplitude. Moreover, we track the real-time evolution of entanglement in the system, which illustrates how particle creation and entanglement generation are directly related. Our work represents a first step towards quantum simulation of high-energy theories using atomic physics experiments—the long-term intention is to extend this approach to real-time quantum simulations of non-Abelian lattice gauge theories.

Nature 534 516 doi: 10.1038/nature18318

Quantum paradox of choice: More freedom makes summoning a quantum state harder

on 2016-6-21 2:00pm GMT

Author(s): Emily Adlam and Adrian Kent

The properties of quantum information in space-time can be investigated by studying operational tasks, such as “summoning,” in which an unknown quantum state is supplied at one point and a call is made at another for it to be returned at a third. Hayden and May [arXiv:1210.0913] recently proved nece…

[Phys. Rev. A 93, 062327] Published Tue Jun 21, 2016

on 2016-6-21 9:04am GMT

Authors: Bertrand Berche, Daniel Malterre, Ernesto Medina

We are taught that gauge transformations in classical and quantum mechanics do not change the physics of the problem. Nevertheless here we discuss three broad scenarios where under gauge transformations: (i) conservation laws are not preserved in the usual manner; (ii) non-gauge-invariant quantities can be associated with physical observables; and (iii) there are changes in the physical boundary conditions of the wave function that render it non-single-valued. We give worked examples that illustrate these points, in contrast to general opinions from classic texts. We also give a historical perspective on the development of Abelian gauge theory in relation to our particular points. Our aim is to provide a discussion of these issues at the graduate level.

on 2016-6-21 9:04am GMT

Authors: Maurice de Gosson, Basil Hiley, Eliahu Cohen

The experimental results of Kocsis et al., Mahler et al. and the proposed experiments of Morley et al. show that it is possible to construct “trajectories” in interference regions in a two-slit interferometer. These results call for a theoretical re-appraisal of the notion of a “quantum trajectory” first introduced by Dirac and in the present paper we re-examine this notion from the Bohm perspective based on Hamiltonian flows. In particular, we examine the short-time propagator and the role that the quantum potential plays in determining the form of these trajectories. These trajectories differ from those produced in a typical particle tracker and the key to this difference lies in the active suppression of the quantum potential necessary to produce Mott-type trajectories. We show, using a rigorous mathematical argument, how the active suppression of this potential arises. Finally we discuss in detail how this suppression also accounts for the quantum Zeno effect.

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

on 2016-6-21 8:01am GMT

Teller, Paul (2016) Role-Player Realism. [Preprint]

Appearance of causality in process matrices when performing fixed-basis measurements for two parties

on 2016-6-20 2:00pm GMT

Author(s): Veronika Baumann and Časlav Brukner

The recently developed framework for quantum theory with no global causal order allows for quantum processes in which operations in local laboratories are neither causally ordered nor in a probabilistic mixture of definite causal orders. The causal relation between the laboratories is described by t…

[Phys. Rev. A 93, 062324] Published Mon Jun 20, 2016