Weekly Papers on Quantum Foundations (11)

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.

The Metaphysics of D-CTCs: On the Underlying Assumptions of Deutsch’s Quantum Solution to the Paradoxes of Time Travel

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on 2015-3-14 3:16am GMT

Dunlap, Lucas (2015) The Metaphysics of D-CTCs: On the Underlying Assumptions of Deutsch’s Quantum Solution to the Paradoxes of Time Travel. [Preprint]

On the Common Structure of the Primitive Ontology Approach and the Information-Theoretic Interpretation of Quantum Theory

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on 2015-3-14 3:15am GMT

Dunlap, Lucas (2015) On the Common Structure of the Primitive Ontology Approach and the Information-Theoretic Interpretation of Quantum Theory. [Preprint]

The Philosophy of Quantum Field Theory

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on 2015-3-14 3:09am GMT

Baker, David John (2015) The Philosophy of Quantum Field Theory. [Preprint]

Violation of unitarity by Hawking radiation does not violate energy-momentum conservation. (arXiv:1502.04324v2 [hep-th] UPDATED)

gr-qc updates on arXiv.org

on 2015-3-13 1:55am GMT

Authors: H. Nikolic

An argument by Banks, Susskind and Peskin (BSP), according to which violation of unitarity would violate either locality or energy-momentum conservation, is widely believed to be a strong argument against non-unitarity of Hawking radiation. We find that the whole BSP argument rests on the crucial assumption that the Hamiltonian is not highly degenerate, and point out that this assumption is not satisfied for systems with many degrees of freedom. Using Lindblad equation, we show that high degeneracy of the Hamiltonian allows local non-unitary evolution without violating energy-momentum conservation. Moreover, since energy-momentum is the source of gravity, we argue that energy-momentum is necessarily conserved for a large class of non-unitary systems with gravity. Finally, we explicitly calculate the Lindblad operators for non-unitary Hawking radiation and show that they conserve energy-momentum.

Bohr-like black holes. (arXiv:1503.03474v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-3-13 1:55am GMT

Authors: Christian Corda

The idea that black holes (BHs) result in highly excited states representing both the “hydrogen atom” and the “quasi-thermal emission” in quantum gravity is today an intuitive but general conviction. In this paper it will be shown that such an intuitive picture is more than a picture. In fact, we will discuss a model of quantum BH somewhat similar to the historical semi-classical model of the structure of a hydrogen atom introduced by Bohr in 1913. The model is completely consistent with existing results in the literature, starting from the celebrated result of Bekenstein on the area quantization.

Short-time quantum propagator and Bohmian trajectories

ScienceDirect Publication: Physics Letters A

on 2015-3-12 10:41am 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.

Quantum Mechanics and Paradigm Shifts

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on 2015-3-11 6:58pm GMT

Allori, Valia (2015) Quantum Mechanics and Paradigm Shifts. [Published Article]

Radiation from a collapsing object is manifestly unitary. (arXiv:1503.01487v1 [gr-qc] CROSS LISTED)

hep-th updates on arXiv.org

on 2015-3-10 12:48am GMT

Authors: Anshul SainiDejan Stojkovic

The process of gravitational collapse excites the fields propagating in the background geometry and gives rise to thermal radiation. We demonstrate by explicit calculations that the density matrix corresponding to such radiation actually describes a pure state. While Hawking’s leading order density matrix contains only the diagonal terms, we calculate the off-diagonal correlation terms. These correlations start very small, but then grow in time. The cumulative effect is that the correlations become comparable to the leading order terms and significantly modify the density matrix. While the trace of the Hawking’s density matrix squared goes from unity to zero during the evolution, the trace of the total density matrix squared remains unity at all times and all frequencies. This implies that the process of radiation from a collapsing object is unitary.

The Other de Broglie Wave. (arXiv:1503.02534v1 [physics.hist-ph])

physics.hist-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

Authors: Daniel Shanahan

In his famous doctoral dissertation, de Broglie assumed that a massive particle is surrounded in its rest frame by a standing wave. He argued that as observed from another inertial frame this wave becomes the superluminal wave now known as the de Broglie wave. It is shown here that under a Lorentz transformation, such a standing wave becomes, not the de Broglie wave, but a modulated wave moving at the velocity of the particle. It is the modulation that has the superluminal velocity of the de Broglie wave and should be recognized as the true de Broglie wave. De Broglie’s demonstrations relied, variously, on his “theorem of the harmony of phases”, on a mechanical model, and on a spacetime diagram. It is shown that in each case the underlying wave was inadvertently suppressed. Identified as a modulation, the de Broglie wave acquires a physically reasonable ontology, avoiding the awkward device of recovering the particle velocity from a superposition of such waves. The deeper wave structure implied by this de Broglie wave must also impinge on such issues in quantum mechanics as the meaning of the wave function and the nature of wave-particle duality.

A Matter of Principle: The Principles of Quantum Theory, Dirac’s Equation, and Quantum Information. (arXiv:1503.02229v1 [physics.hist-ph])

physics.hist-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

This article is concerned with the role of fundamental principles in theoretical physics, especially quantum theory. The fundamental principles of relativity will be be addressed as well in view of their role in quantum electrodynamics and quantum field theory, specifically Dirac’s work, which, in particular Dirac’s derivation of his relativistic equation for the electron from the principles of relativity and quantum theory, is the main focus of this article. I shall, however, also consider Heisenberg’s derivation of quantum mechanics, which inspired Dirac. I argue that Heisenberg’s and Dirac’s work alike was guided by their adherence to and confidence in the fundamental principles of quantum theory. The final section of the article discusses the recent work by G. M. D’ Ariano and his coworkers on the principles of quantum information theory, which extends quantum theory and its principles in a new direction. This extension enabled them to offer a new derivation of Dirac’s equation from these principles alone, without using the principles of relativity.

Quantum Information Biology: from information interpretation of quantum mechanics to applications in molecular biology and cognitive psychology. (arXiv:1503.02515v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

We discuss foundational issues of quantum information biology (QIB) — one of the most successful applications of the quantum formalism outside of physics. QIB provides a multi-scale model of information processing in bio-systems: from proteins and cells to cognitive and social systems. This theory has to be sharply distinguished from “traditional quantum biophysics”. The latter is about quantum bio-physical processes, e.g., in cells or brains. QIB models the dynamics of information states of bio-systems. It is based on the quantum-like paradigm: complex bio-systems process information in accordance with the laws of quantum information and probability. This paradigm is supported by plenty of statistical bio-data collected at all scales, from molecular biology and genetics/epigenetics to cognitive psychology and behavioral economics. We argue that the information interpretation of quantum mechanics (its various forms were elaborated by Zeilinger and Brukner, Fuchs and Mermin, and D’ Ariano) is the most natural interpretation of QIB. We also point out that QBIsm (Quantum Bayesianism) can serve to find a proper interpretation of bio-quantum probabilities. Biologically QIB is based on two principles: a) adaptivity; b) openness (bio-systems are fundamentally open). These principles are mathematically represented in the framework of a novel formalism — quantum adaptive dynamics which, in particular, contains the standard theory of open quantum systems as a special case of adaptivity (to environment).

Macroscopic quantum resonators (MAQRO): 2015 Update. (arXiv:1503.02640v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

Do the laws of quantum physics still hold for macroscopic objects – this is at the heart of Schr\”odinger’s cat paradox – or do gravitation or yet unknown effects set a limit for massive particles? What is the fundamental relation between quantum physics and gravity? Ground-based experiments addressing these questions may soon face limitations due to limited free-fall times and the quality of vacuum and microgravity. The proposed mission MAQRO may overcome these limitations and allow addressing those fundamental questions. MAQRO harnesses recent developments in quantum optomechanics, high-mass matter-wave interferometry as well as state-of-the-art space technology to push macroscopic quantum experiments towards their ultimate performance limits and to open new horizons for applying quantum technology in space. The main scientific goal of MAQRO is to probe the vastly unexplored “quantum-classical” transition for increasingly massive objects, testing the predictions of quantum theory for truly macroscopic objects in a size and mass regime unachievable in ground-based experiments. The hardware for the mission will largely be based on available space technology. Here, we present the MAQRO proposal submitted in response to the (M4) Cosmic Vision call of the European Space Agency for a medium-size mission opportunity with a possible launch in 2025.

Proof of a Conjecture on Contextuality in Cyclic Systems with Binary Variables. (arXiv:1503.02181v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

Authors: Janne V. KujalaEhtibar N. Dzhafarov

We present a proof for a conjecture previously formulated by Dzhafarov, Kujala, and Larsson (Foundations of Physics, in press,arXiv:1411.2244). The conjecture specifies a measure for degree of contextuality and a criterion (necessary and sufficient condition) for contextuality in a broad class of quantum systems. This class includes Leggett-Garg, EPR/Bell, and Klyachko-Can-Binicioglu-Shumovsky type systems as special cases. In a system of this class certain physical properties $q_{1},\ldots,q_{n}$ are measured in pairs $\left(q_{i},q_{j}\right)$; every property enters in precisely two such pairs; and each measurement outcome is a binary random variable. Denoting the measurement outcomes for a property $q_{i}$ in the two pairs it enters by $V_{i}$ and $W_{i}$, the pair of measurement outcomes for $\left(q_{i},q_{j}\right)$ is $\left(V_{i},W_{j}\right)$. Contextuality is defined as follows: one computes the minimal possible value $\Delta_{0}$ for the sum of $\Pr\left[V_{i}\not=W_{i}\right]$ (over $i=1,\ldots,n$) that is allowed by the individual distributions of $V_{i}$ and $W_{i}$; one computes the minimal possible value $\Delta_{\min}$ for the sum of $\Pr\left[V_{i}\not=W_{i}\right]$ across all possible couplings of (i.e., joint distributions imposed on) the entire set of random variables $V_{1},W_{1},\ldots,V_{n},W_{n}$ in the system; and the systems is considered contextual if $\Delta_{\min}>\Delta_{0}$ (otherwise $\Delta_{\min}=\Delta_{0}$). This definition has its justification in the general approach dubbed Contextuality-by-Default, and it allows for measurement errors and signaling among the measured properties. The conjecture proved in this paper specifies the value of $\Delta_{\min}-\Delta_{0}$ in terms of the distributions of the measurement outcomes $\left(V_{i},W_{j}\right)$.

Localization by Dissipative Disorder: a Deterministic Approach to Position Measurements. (arXiv:1503.02494v1 [cond-mat.quant-gas])

quant-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

Authors: Giovanni BarontiniVera Guarrera

We propose an approach to position measurements based on the hypothesis that the action of a position detector on a quantum system can be effectively described by a dissipative disordered potential. We show that such kind of potential is able, via the dissipation-induced Anderson localization, to contemporary localize the wavefunction of the system and to dissipate information to modes bounded to the detector. By imposing a diabaticity condition we demonstrate that the dissipative dynamics between the modes of the system leads to a localized energy exchange between the detector and the rest of the environment -the “click” of the detector- thus providing a complete deterministic description of a position measurement. We finally numerically demonstrate that our approach is consistent with the Born probability rule.

The equivalent emergence of time dependence in classical and quantum mechanics. (arXiv:1503.02146v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-3-10 12:48am GMT

Authors: John S. Briggs

Beginning with the principle that a closed mechanical composite system is timeless, time can be de?ned by the regular changes in a suitable position coordinate (clock) in the observing part, when one part of the closed composite observes another part. Translating this scenario into both classical and quantum mechanics allows a transition to be made from a time-independent mechanics for the closed composite to a time-dependent description of the observed part alone. The use of Hamilton- Jacobi theory yields a very close parallel between the derivations in classical and quantum mechanics. The time-dependent equations, Hamilton-Jacobi or Schrodinger, appear as approximations since no observed system is truly closed. The quantum case has an additional feature in the condition that the observing environment must become classical in order to de?ne a real classical time variable. This condition leads to a removal of entanglement engendered by the interaction between the observed system and the observing environment. Comparison is made to the similar emergence of time in quantum gravity theory

Primitive ontology and quantum field theory

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on 2015-3-09 11:48pm GMT

Lam, Vincent (2015) Primitive ontology and quantum field theory. [Preprint]