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.

Holographic Signatures of Cosmological Singularities. (arXiv:1404.2309v3 [hep-th] UPDATED)

on 2014-11-21 9:07am GMT

Authors: Netta Engelhardt, Thomas Hertog, Gary T. Horowitz

To gain insight in the quantum nature of cosmological singularities, we study anisotropic Kasner solutions in gauge/gravity duality. The dual description of the bulk evolution towards the singularity involves N = 4 super Yang-Mills on the expanding branch of deformed de Sitter space and is well defined. We compute two-point correlators of Yang-Mills operators of large dimensions using spacelike geodesics anchored on the boundary. The correlators show a strong signature of the singularity around horizon scales and decay at large boundary separation at different rates in different directions. More generally, the boundary evolution exhibits a process of particle creation similar to that in inflation. This leads us to conjecture that information on the quantum nature of cosmological singularities is encoded in long-wavelength features of the boundary wave function.

Incompleteness of measurement apparatuses. (arXiv:1411.5524v1 [quant-ph])

on 2014-11-21 9:07am GMT

Authors: Petr Hajicek

A complete apparatus is defined as reacting to every state of the measured system. Standard quantum mechanics of indistinguishable particles is shown to imply that apparatuses must be incomplete or else they would be drowned out by noise. Each quantum observable is then an abstract representation of many measurement apparatuses. Moreover, the measured systems must be prepared in a state that is sufficiently different from the states of particles in the environment. This is the main purpose of preparations. A system so prepared was said to have a “separation status”. A new, more satisfactory definition of separations status is given than that proposed in previous papers. Conditions are specified under which the particles in the environment may be ignored as is usually done in the theory of measurement.

Classical and quantum cosmology with York time

Classical and Quantum Gravity – latest papers

on 2014-11-21 12:00am GMT

We consider a solution to the problem of time in quantum gravity by deparameterization of the ADM action in terms of York time, a parameter proportional to the extrinsic curvature of a spatial hypersurface. We study a minisuperspace model together with a homogeneous scalar field, for which we can solve the Hamiltonian constraint exactly and arrive at an explicit expression for the physical (non-vanishing) Hamiltonian. The scale factor and associated momentum cease to be dynamical variables, leaving the scalar field as the only physical degree of freedom. We investigate the resulting classical theory, showing how the dynamics of the scale factor can be recovered via an appropriate interpretation of the Hamiltonian as a volume. We then quantize the system in the Schrödinger picture. In the quantum theory we recover the dynamics of the scale factor by interpreting the spectrum and expectation value of the Hamiltonian as being associated with volume rather than energy. If trajectorie…

Can quantum systems succumb to their own (gravitational) attraction?

Classical and Quantum Gravity – latest papers

on 2014-11-21 12:00am GMT

The gravitational interaction is generally considered to be too weak to be easily submitted to systematic experimental investigation in the quantum, microscopic, domain. In this paper we attempt to remedy this situation by considering the gravitational influence exerted by a crystalline nanosphere of mesoscopic size on itself, in the semi-classical, mean field, regime. We study in depth the self-localization process induced by the corresponding nonlinear potential of (gravitational) self-interaction. In particular, we characterize the stability of the associated self-collapsed ground state and estimate the magnitude of the corrections that are due to the internal structure of the object (this includes size-effects and corrections due to the discrete, atomic, structure of the sphere). Finally, we derive an approximated, Gaussian, dynamics which mimics several essential features of the self-gravitating dynamics and, based on numerical results derived from this model, we propose a c…

Origin of probabilities and their application to the multiverse. (arXiv:1212.0953v3 [gr-qc] UPDATED)

on 2014-11-20 12:54pm GMT

Authors: Andreas Albrecht, Daniel Phillips

We argue using simple models that all successful practical uses of probabilities originate in quantum fluctuations in the microscopic physical world around us, often propagated to macroscopic scales. Thus we claim there is no physically verified fully classical theory of probability. We comment on the general implications of this view, and specifically question the application of classical probability theory to cosmology in cases where key questions are known to have no quantum answer. We argue that the ideas developed here may offer a way out of the notorious measure problems of eternal inflation.

John Bell and the Nature of the Quantum World. (arXiv:1411.5322v1 [physics.hist-ph])

physics.hist-ph updates on arXiv.org

on 2014-11-20 12:54pm GMT

Authors: Reinhold A. Bertlmann

I present my encounter with John Bell at CERN, our collaboration and joint work in particle physics. I also will recall our quantum debates and give my personal view on Bell’s fundamental work on quantum theory, in particular, on contextuality and nonlocality of quantum physics. Some mathematical and geometric aspects of entanglement are discussed as influence of Bell’s Theorem. Finally, I make some historical comments on the experimental side of Bell inequalities.

on 2014-11-20 12:54pm GMT

Authors: Simon A. Haine, Stuart S. Szigeti, Matthias D. Lang, Carlton M. Caves

Information recycling has been shown to improve the sensitivity of interferometers when the input quantum state has been partially transferred from some donor system. In this paper we demonstrate that when the quantum state of this donor system is from a particular class of Heisenberg-limited states, information recycling yields a Heisenberg-limited phase measurement. Crucially, this result holds irrespective of the fraction of the quantum state transferred to the interferometer input and also for a general class of number-conserving quantum-state-transfer processes, including ones that destroy the first-order phase coherence between the branches of the interferometer. This result could have significant applications in Heisenberg-limited atom interferometry, where the quantum state is transferred from a Heisenberg-limited photon source, and in optical interferometry where the loss can be monitored.

Experimental Bounds on Classical Random Field Theories. (arXiv:1411.5056v1 [quant-ph])

on 2014-11-20 12:54pm GMT

Authors: Joffrey K. Peters, Jingyun Fan, Alan L. Migdall, Sergey V. Polyakov

Alternative theories to quantum mechanics motivate important fundamental tests of our understanding and descriptions of the smallest physical systems. Here, using spontaneous parametric downconversion as a heralded single-photon source, we place experimental limits on a class of alternative theories, consisting of classical field theories which result in power-dependent normalized correlation functions. In addition, we compare our results with standard quantum mechanical interpretations of our spontaneous parametric downconversion source over an order of magnitude in intensity. Our data match the quantum mechanical expectations, and do not show a statistically significant dependence on power, limiting on quantum mechanics alternatives which require power-dependent autocorrelation functions.

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

on 2014-11-20 3:00am GMT

Lombardi, Olimpia and Holik, Federico and Vanni, Leonardo (2014) What is quantum information? [Preprint]

on 2014-11-18 6:07am GMT

Authors: Agata Chȩcińska, Andrzej Dragan

We show how to reliably encode quantum information and send it between two arbitrary general-relativistic observers without a shared reference frame. Any information stored in a quantum field will inevitably be destroyed by an unknown Bogolyubov transformation relating the observers. However certain quantum correlations between different, independent fields will be preserved, no matter what transformation is applied. We show how to efficiently use these correlations in communication between arbitrary observers.

Jerusalem Lectures on Black Holes and Quantum Information. (arXiv:1409.1231v2 [hep-th] UPDATED)

on 2014-11-18 6:07am GMT

Authors: Daniel Harlow

In these lectures I give an introduction to the quantum physics of black holes, including recent developments based on quantum information theory such as the firewall paradox and its various cousins. I also give an introduction to holography and the AdS/CFT correspondence, focusing on those aspects which are relevant for the black hole information problem.

Where to Apply Relationalism. (arXiv:1411.4316v1 [gr-qc])

on 2014-11-18 6:07am GMT

Authors: Edward Anderson

Relationalism — along the lines developed by Barbour and collaborators in the past 3 decades — can be considered an advance with 1/4 of the facets of the canonical approach’s Problem of Time as identified by Isham and Kuchar. Indeed, almost all of the Problem of Time facets have classical counterparts, since they arise from consequences of demanding background independence rather than about combining GR and QM per se. Moreover the quantum version is harder, while the classical counterpart provides some suggestions through being more solvable. The suggestion then is to consider the effect of this advance on the Problem of Time as a whole, as opposed to repeating the same classical portion for a different redundancy group acting on the configuration space: shape dynamics. There are indeed some knock-on effects because the facets are notoriously not independent. The other facets do also however require distinct insights. Finally, I comment on the above being `metric’ background independence, whereas quantum gravity usually assumes many other levels of background structures. Whilst Isham already wrote about this over two decades ago, it has largely not yet been incorporated into quantum gravity programs, and could well be a good area to extend and re-envigour by use of relational thinking.

on 2014-11-18 6:06am GMT

Authors: Elliott Tammaro

The stability of dynamical systems against perturbations (variations in initial conditions/model parameters) is a property referred to as structural stability. The study of sensitivity to perturbation is essential because in experiment initial conditions are not fixed, nor are model parameters known, to arbitrarily high precision. Additionally, if a physical system under study exhibits stability (insensitivity to initial conditions) then a theoretical description of the system must exhibit structural stability. Consequently, stability can be a useful indicator of the correctness of a theoretical formulation. In this work the many-worlds interpretation is considered. It is first demonstrated that the interpretation admits a class of special states, herein referred to as “quantum liar states,” because they indicate disagreement between the recorded result of a measurement and the actual state of a system. It is then demonstrated that the many-worlds interpretation is not structurally stable against the introduction of quantum liar states.

on 2014-11-18 6:06am GMT

Authors: Sania Jevtic, Terry Rudolph

We show how one can be led from considerations of quantum steering to Bell’s theorem. We begin with Einstein’s demonstration that, assuming locality, quantum states must be in a many-to-one (“incomplete”) relationship with the real physical states of the system. We then consider some simple constraints that locality imposes on any such incomplete model of physical reality, and show they are not satisfiable. Historically this is not how Bell’s theorem arose – there are slight and subtle differences in the arguments – but it could have been.

on 2014-11-18 6:06am GMT

Authors: Lajos Diósi

We show that the heating effect of spontaneous wave-function collapse models implies an experimentally significant increment $\Delta T$ of equilibrium temperature in a mechanical oscillator. The obtained form $\Delta T$ is linear in the oscillator’s relaxation time $\tau$ and independent of the mass. The oscillator can be in a classical thermal state, the effect $\Delta T$ is classical for a wide range of frequencies and quality factors. We note that the test of $\Delta T$ does not necessitate quantum state monitoring but tomography. In both gravity-related (DP) and continuous spontaneous localization (CSL) models the strong-effect edge of their parameter range can be challenged in existing experiments on classical oscillators. For the CSL theory, the conjectured highest collapse rate parameter values become immediately constrained by evidences from current experiments on extreme slow-ring-down oscillators.

Imprecise probability for non-commuting observables. (arXiv:1411.4319v1 [quant-ph])

on 2014-11-18 6:06am GMT

Authors: A. E. Allahverdyan

It is known that non-commuting observables in quantum mechanics do not have joint probability. This statement refers to the precise (additive) probability model. I show that the joint distribution of any non-commuting pair of variables can be quantified via upper and lower probabilities, i.e. the joint probability is described by an interval instead of a number (imprecise probability). I propose transparent axioms from which the upper and lower probability operators follow. They depend only on the non-commuting observables and revert to the usual expression for the commuting case.

Quantum Potential Energy as Concealed Motion

Latest Results for Foundations of Physics

on 2014-11-18 12:00am GMT

Abstract

It is known that the Schrödinger equation may be derived from a hydrodynamic model in which the Lagrangian position coordinates of a continuum of particles represent the quantum state. Using Routh’s method of ignorable coordinates it is shown that the quantum potential energy of particle interaction that represents quantum effects in this model may be regarded as the kinetic energy of additional ‘concealed’ freedoms. The method brings an alternative perspective to Planck’s constant, which plays the role of a hidden variable, and to the canonical quantization procedure, since what is termed ‘kinetic energy’ in quantum mechanics may be regarded literally as energy due to motion.

Quantum equivalence, the second law and emergent gravity. (arXiv:1411.3901v1 [quant-ph])

on 2014-11-17 1:30am GMT

Authors: Dries Sels, Michiel Wouters

Since the advent of quantum mechanics we have mainly been concerned with its predictions from the perspective of an external observer. This is in strong contrast to the theory of general relativity, where the physics is governed by the intrinsic properties of space-time. At the same time, the precise relation between space-time and quantum mechanics is still one of the greatest problems of theoretical physics. This immediately raises the question on the completeness of our understanding of quantum mechanics. Here we address the problem by making an intrinsic analysis of observables in generic quantum systems. We show that there is an extreme fine tuning problem for the emergence of physics from the Hilbert space dynamics. However, for any initial condition and Hamiltonian, there exists a special set of observables. We show that these observables are intimately linked to the natural configuration space in which an area law for the entanglement is inevitable. We argue that this implies emergent gravity.

Quantum field theory of relic nonequilibrium systems. (arXiv:1409.6817v2 [hep-th] UPDATED)

on 2014-11-17 1:30am GMT

Authors: Nicolas G. Underwood, Antony Valentini

In terms of the de Broglie-Bohm pilot-wave formulation of quantum theory, we develop field-theoretical models of quantum nonequilibrium systems which could exist today as relics from the very early universe. We consider relic excited states generated by inflaton decay, as well as relic vacuum modes, for particle species that decoupled close to the Planck temperature. Simple estimates suggest that, at least in principle, quantum nonequilibrium could survive to the present day for some relic systems. The main focus of this paper is to describe the behaviour of such systems in terms of field theory, with the aim of understanding how relic quantum nonequilibrium might manifest experimentally. We show by explicit calculation that simple perturbative couplings will transfer quantum nonequilibrium from one field to another (for example from the inflaton field to its decay products). We also show that fields in a state of quantum nonequilibrium will generate anomalous spectra for standard energy measurements. Possible connections to current astrophysical observations are briefly addressed.

The Quantum Hall Effects: Philosophical Approach. (arXiv:1406.4427v2 [physics.hist-ph] UPDATED)

physics.hist-ph updates on arXiv.org

on 2014-11-17 1:30am GMT

Authors: Pascal Lederer

The Quantum Hall Effects offer a rich variety of theoretical and experimental advances. They provide interesting insights on such topics as complementarity, gauge invariance, strong interactions, emergence of new theoretical concepts. This paper focuses on some related philosophical questions. Hacking’s views on Scientific Realism, Chalmers’ on Non Figurative Realism are discussed. It is argued that the difficulties with those versions of realism may be resolved within a dialectical materialist approach. The latter is shown to provide a rational approach to the phenomena, the theory and the ontology of the Quantum Hall Effects.

on 2014-11-17 1:30am GMT

Authors: Alex Matzkin

Weak values, obtained from weak measurements, attempt to describe the properties of a quantum system as it evolves from an initial to a final state, without practically altering this evolution. Trajectories can be defined from weak measurements of the position, or inferred from weak values of the momentum operator. The former can be connected to the asymptotic form of the Feynman propagator and the latter to Bohmian trajectories. Employing a time-dependent oscillator as a model, this work analyzes to what extent weak measurements can shed light on the underlying dynamics of a quantum system expressed in terms of trajectories, in particular by comparing the two approaches.

on 2014-11-17 1:30am GMT

Authors: Roderick I. Sutherland

A Lagrangian description is presented here that can be used in conjunction with a particle interpretation of quantum mechanics. The advantages of this description are that the field equations and the particle equations of motion can both be deduced from a single Lagrangian density expression and that conservation of energy and momentum are assured. This Lagrangian formulation is then applied to the special case of the well-known Bohm model as an example. It is thereby demonstrated that such a formulation is compatible with the predictions of quantum mechanics.