Weekly Papers on Quantum Foundations (28)

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.

Consciousness and Quantum Measurement

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on 2016-7-08 6:27pm GMT

Broka, Chris (2016) Consciousness and Quantum Measurement. [Preprint]

The universe remembers no wavefunction collapse. (arXiv:1607.02076v1 [quant-ph])

physics.hist-ph updates on arXiv.org

on 2016-7-08 11:56am GMT

Authors: Ovidiu Cristinel Stoica

Two thought experiments are analyzed, revealing that the quantum state of the universe does not contain evidence of the wavefunction collapse. The first thought experiment shows that unitary quantum evolution alone can account for the outcomes of any combination of quantum experiments. This is in contradiction with the standard view on quantum measurement, which appeals to the wavefunction collapse. The second thought experiment consists in successive measurements, and reveals that the standard quantum measurement scheme predicts violations of the conservation laws. It is shown that the standard view on quantum measurements makes some unnecessary assumptions, which lead to the apparent necessity to invoke wavefunction collapse. Once these assumptions are removed, a new measurement scheme emerges, which is compatible with both the unitary evolution and the conservation laws.

Time symmetry in wave function collapse. (arXiv:1607.01940v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-08 11:55am GMT

Authors: Daniel BedinghamOwen Maroney

The notion of a physical collapse of the wave function is embodied in dynamical collapse models. These involve a modification of the unitary evolution of the wave function such as to give a dynamical account of collapse. The resulting dynamics is at first sight time asymmetric for the simple reason that the wave function depends on those collapse events in the past but not those in the future. Here we show that dynamical wave function collapse models admit a general description that has no inbuilt direction of time. Given some simple constraints, we show that there exist empirically equivalent pictures of collapsing wave functions in both time directions, each satisfying the same dynamical rules. A preferred direction is singled out only by the asymmetric initial and final time constraints on the state of the Universe.

The logic of the future in quantum theory

Latest Results for Synthese

on 2016-7-08 12:00am GMT

Abstract

According to quantum mechanics, statements about the future made by sentient beings like us are, in general, neither true nor false; they must satisfy a many-valued logic. I propose that the truth value of such a statement should be identified with the probability that the event it describes will occur. After reviewing the history of related ideas in logic, I argue that it gives an understanding of probability which is particularly satisfactory for use in quantum mechanics. I construct a lattice of future-tense propositions, with truth values in the interval [0, 1], and derive logical properties of these truth values given by the usual quantum-mechanical formula for the probability of a history.

[Editors’ Choice] How a particle gets its quantum kicks

Science: Current Issue

on 2016-7-08 12:00am GMT

Author: Ian S. Osborne

Local Causality in a Friedmann-Robertson-Walker Spacetime

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

on 2016-7-07 7:31pm GMT

Christian, Joy (2016) Local Causality in a Friedmann-Robertson-Walker Spacetime. [Published Article or Volume]

Dirac’s Prediction of the Positron: A Case Study for the Current Realism Debate

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on 2016-7-07 7:20pm GMT

Pashby, Thomas (2012) Dirac’s Prediction of the Positron: A Case Study for the Current Realism Debate. [Published Article or Volume]

Coarse-Graining as a Route to Microscopic Physics: The Renormalization Group in Quantum Field Theory

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

on 2016-7-07 7:19pm GMT

Leif, Hancox-Li (2014) Coarse-Graining as a Route to Microscopic Physics: The Renormalization Group in Quantum Field Theory. [Published Article or Volume]

Structural features of sequential weak measurements

PRA: Fundamental concepts

on 2016-7-07 2:00pm GMT

Author(s): Lajos Diósi

We discuss the abstract structure of sequential weak measurement (WM) of general observables. In all orders, the sequential WM correlations without postselection yield the corresponding correlations of the Wigner function, offering direct quantum tomography through the moments of the canonical varia…

 

[Phys. Rev. A 94, 010103(R)] Published Thu Jul 07, 2016

Global versus Local — Mach’s Principle versus the Equivalence Principle. (arXiv:1607.01442v1 [gr-qc])

gr-qc updates on arXiv.org

on 2016-7-07 10:16am GMT

Authors: Douglas SingletonSteve Wilburn

The equivalence principle is the conceptual basis for general relativity. In contrast Mach’s principle, although said to have been influential on Einstein in his formulation of general relativity, has not been shown to be central to the structure of general relativity. In this essay we suggest that the quantum effects of Hawking and Unruh radiation are a manifestation of a {\it thermal} Mach’s principle, where the local thermodynamic properties of the system are determined by the non-local structure of the quantum fields which determine the vacuum of a given spacetime. By comparing Hawking and Unruh temperatures for the same local acceleration we find a violation of the Einstein elevator version of the equivalence principle, which vanishes in the limit that the horizon is approached.

On the origin of nonclassicality in single systems. (arXiv:1607.01768v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-07 10:16am GMT

Authors: S. AravindaR. SrikanthAnirban Pathak

Investigating the foundational basis underpinning nonclassicality in an operational theory of single (i.e., monopartite), finite-dimensional systems in the convex framework, we show that many significant nonclassical features of quantum mechanics can be derived from two axioms– (a) Pairwise \textit{incongruence} among $m$ observables, leading to the non-simpliciality of the state space; (b) Prohibition of $m$-congruence associated with an intransitive or unextendable congruence structure, when $m>2$.– Axiom (a) suffices to derive a host of nonclassical features, among them, multiple pure-state decomposability, non-comeasurability, measurement disturbance, no-cloning, unconditional cryptographic security as well as (with minor provisos) uncertainty, preparation contextuality and the impossibility of certain coherent operations such as the universal inverter. The major feature not derivable from axiom (a) is Kochen-Specker contextuality, for which axiom (b) is necessary, and which can serve as the basis for a kind of device-independent cryptographic security. Our approach also allows for non-quantum nonclassicality wherein axiom (b) holds without (a) being true, corresponding to higher-order contextual correlations.

Comment on Adler’s “Does the Peres experiment using photons test for hyper-complex (quaternionic) quantum theories?”. (arXiv:1607.01648v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-07 10:16am GMT

Authors: Lorenzo M. ProcopioLee A. RozemaBorivoje DakićPhilip Walther

In his recent article [arXiv:1604.04950], Adler questions the usefulness of the bound found in our experimental search for genuine effects of hyper-complex quantum mechanics [arXiv:1602.01624]. Our experiment was performed using a black-box (instrumentalist) approach to generalized probabilistic theories; therefore, it does not assume a priori any particular underlying mechanism. From that point of view our experimental results do indeed place meaningful bounds on possible effects of “post-quantum theories”, including quaternionic quantum mechanics. In his article, Adler compares our experiment to non-relativistic and M\”oller formal scattering theory within quaternionic quantum mechanics. With a particular set of assumptions, he finds that quaternionic effects would likely not manifest themselves in general. Although these assumptions are justified in the non-relativistic case, a proper calculation for relativistic particles is still missing. Here, we provide a concrete relativistic example of Klein-Gordon scattering wherein the quaternionic effects persist. We note that when the Klein-Gordon equation is formulated using a Hamiltonian formalism it displays a so-called “indefinite metric”, a characteristic feature of relativistic quantum wave equations. In Adler’s example this is directly forbidden by his assumptions, and therefore our present example is not in contradiction to his work. In complex quantum mechanics this problem of an indefinite metric is solved in second quantization. Unfortunately, there is no known algorithm for canonical field quantization in quaternionic quantum mechanics.

Coherent state of Light is Nonclassical: Irreducibility. (arXiv:1607.01576v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-07 10:16am GMT

Authors: Jeongwoo JaeKang Hee SeolKwang-Geol LeeJinhyoung Lee

We suggest an optical method which tests a nonclassical feature with a coherent state input. The test is designed with multiplexing of on/off detectors and post-selection. We adopt the sub-binomiality as a nonclassical feature, replacing Mandel’s $Q$-factor. The sub-binomiality is negative even for coherent states when the post-selection is made. However, we show that it can be reproduced by a classical model with the on/off detectors. In the sense, the sub-binomiality is unlikely to identify the genuine nonclassicality. On the other hand, we propose a coincident probability of first two branches and show that the classical model fails to reproduce the quantum coincident probability. The failure of the classical model results from the classical description of light, i.e. the divisibility of intensity into parts no matter how small it is. Then our optical test identifies a nonclassical feature of coherent states against the classical divisibility of light, which is said irreducibility.

Verifying quantum superpositions at metre scales. (arXiv:1607.01454v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-07 10:16am GMT

Authors: Dan M. Stamper-KurnG. Edward MartiHolger Müller

While the existence of quantum superpositions of massive particles over microscopic separations has been established since the birth of quantum mechanics, the maintenance of superposition states over macroscopic separations is a subject of modern experimental tests. In Ref. [1], T. Kovachy et al. report on applying optical pulses to place a freely falling Bose-Einstein condensate into a superposition of two trajectories that separate by an impressive distance of 54 cm before being redirected toward one another. When the trajectories overlap, a final optical pulse produces interference with high contrast, but with random phase, between the two wave packets. Contrary to claims made in Ref. [1], we argue that the observed interference is consistent with, but does not prove, that the spatially separated atomic ensembles were in a quantum superposition state. Therefore, the persistence of such superposition states remains experimentally unestablished.

Novel Principles and the Charge-Symmetric Design of Dirac’s Quantum Mechanics: I. Enhanced Eriksen’s Theorem and the Universal Charge-Index Formalism for Dirac’s Equation in (Strong) External Static Fields

Latest Results for Foundations of Physics

on 2016-7-07 12:00am GMT

Abstract

The presented enhanced version of Eriksen’s theorem defines an universal transform of the Foldy–Wouthuysen type and in any external static electromagnetic field (ESEMF) reveals a discrete symmetry of Dirac’s equation (DE), responsible for existence of a highly influential conserved quantum number—the charge index distinguishing two branches of DE spectrum. It launches the charge-index formalism (CIF) obeying the charge-index conservation law (CICL). Via its unique ability to manipulate each spectrum branch independently, the CIF creates a perfect charge-symmetric architecture of Dirac’s quantum mechanics (DQM), which resolves all the riddles of the standard DE theory (SDET). Besides the abstract CIF algebra, the paper discusses: (1) the novel accurate charge-symmetric definition of the electric-current density; (2) DE in the true-particle representation, where electrons and positrons coexist on equal footing; (3) flawless “natural” scheme of second quantization; and (4) new physical grounds for the Fermi–Dirac statistics. As a fundamental quantum law, the CICL originates from the kinetic-energy sign conservation and leads to a novel single-particle physics in strong-field situations. Prohibiting Klein’s tunneling (KT) in Klein’s zone via the CICL, the precise CIF algebra defines a new class of weakly singular DE solutions, strictly confined in the coordinate space and experiencing the total reflection from the potential barrier.

Perfect Quantum Cosmological Bounce

PRL Editors’ Suggestions

on 2016-7-06 2:00pm GMT

Author(s): Steffen Gielen and Neil Turok

One theory for the formation of the universe replaces the singularity of the big bang with a smooth quantum “bounce”. This theory is extended to account for the passage of density variations and gravitational waves across the bounce.

[Phys. Rev. Lett. 117, 021301] Published Wed Jul 06, 2016

Generalized Uncertainty Principle and Angular Momentum. (arXiv:1607.01083v1 [gr-qc])

hep-th updates on arXiv.org

on 2016-7-06 4:50am GMT

Authors: Pasquale BossoSaurya Das

Various models of quantum gravity suggest a modification of the Heisenberg’s Uncertainty Principle, to the so-called Generalized Uncertainty Principle, between position and momentum. In this work we show how this modification influences the theory of angular momentum in Quantum Mechanics. In particular, we compute Planck scale corrections to angular momentum eigenvalues, the Hydrogen atom spectrum, the Stern-Gerlach experiment and the Clebsch-Gordan coefficients. We also examine effects of the Generalized Uncertainty Principle on multi-particle systems.

Do Horizons Exist?. (arXiv:1607.01286v1 [hep-th])

hep-th updates on arXiv.org

on 2016-7-06 4:50am GMT

Authors: Davood Allahbakhshi

Gravitational effective action is calculated to second order in transverse momentums for a planar asymptotically anti-de Sitter geometry by gauge fixing method. The first order bulk energy-momentum tensor is calculated. The zeroth order equations of motion are solved and a new black brane-like solution is found. We show that once the contribution of matter quantum modes is taken into account, the horizon of the black brane disappears. This is also correct for BTZ black hole. Our result strengthens the black hole non-existence proposal by Hawking.

Observables, gravitational dressing, and obstructions to locality and subsystems. (arXiv:1607.01025v1 [hep-th])

hep-th updates on arXiv.org

on 2016-7-06 4:50am GMT

Authors: William DonnellySteven B. Giddings

Quantum field theory – our basic framework for describing all non-gravitational physics – conflicts with general relativity: the latter precludes the standard definition of the former’s essential principle of locality, in terms of commuting local observables. We examine this conflict more carefully, by investigating implications of gauge (diffeomorphism) invariance for observables in gravity. We prove a dressing theorem, showing that any operator with nonzero Poincare charges, and in particular any compactly-supported operator, in flat-spacetime quantum field theory must be gravitationally dressed once coupled to gravity, i.e. it must depend on the metric at arbitrarily long distances, and we put lower bounds on this nonlocal dependence. This departure from standard locality occurs in the most severe way possible: in perturbation theory about flat spacetime, at leading order in Newton’s constant. The physical observables in a gravitational theory therefore do not organize themselves into local commuting subalgebras: the principle of locality must apparently be reformulated or abandoned, and in fact we lack a clear definition of the coarser and more basic notion of a quantum subsystem of the Universe. We discuss relational approaches to locality based on diffeomorphism-invariant nonlocal operators, and reinforce arguments that any such locality is state-dependent and approximate. We also find limitations to the utility of bilocal diffeomorphism-invariant operators that are considered in cosmological contexts. An appendix provides a concise review of the canonical covariant formalism for gravity, instrumental in the discussion of Poincare charges and their associated long-range fields.

A Quantum Focussing Conjecture. (arXiv:1506.02669v1 [hep-th] CROSS LISTED)

gr-qc updates on arXiv.org

on 2016-7-06 4:50am GMT

Authors: Raphael BoussoZachary FisherStefan Leichenauerand Aron C. Wall

We propose a universal inequality that unifies the Bousso bound with the classical focussing theorem. Given a surface $\sigma$ that need not lie on a horizon, we define a finite generalized entropy $S_\text{gen}$ as the area of $\sigma$ in Planck units, plus the von Neumann entropy of its exterior. Given a null congruence $N$ orthogonal to $\sigma$, the rate of change of $S_\text{gen}$ per unit area defines a quantum expansion. We conjecture that the quantum expansion cannot increase along $N$. This extends the notion of universal focussing to cases where quantum matter may violate the null energy condition. Integrating the conjecture yields a precise version of the Strominger-Thompson Quantum Bousso Bound. Applied to locally parallel light-rays, the conjecture implies a Quantum Null Energy Condition: a lower bound on the stress tensor in terms of the second derivative of the von Neumann entropy. We sketch a proof of this novel relation in quantum field theory.

Black Holes, Information Loss and the Measurement Problem. (arXiv:1607.01255v1 [gr-qc])

gr-qc updates on arXiv.org

on 2016-7-06 4:50am GMT

Authors: Elias OkonDaniel Sudarsky

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. In particular, we will display the strong link between black holes, the issue of information loss and the measurement problem.

Self-locating Uncertainty and the Origin of Probability in Everettian Quantum Mechanics

The British Journal for the Philosophy of Science – Advance Access

on 2016-7-05 8:29am GMT

A longstanding issue in attempts to understand the Everett (many-worlds) approach to quantum mechanics is the origin of the Born rule: why is the probability given by the square of the amplitude? Following Vaidman, we note that observers are in a position of self-locating uncertainty during the period between the branches of the wave function splitting via decoherence and the observer registering the outcome of the measurement. In this period, it is tempting to regard each branch as equiprobable, but we argue that the temptation should be resisted. Applying lessons from this analysis, we demonstrate (using methods similar to those of Zurek’s envariance-based derivation) that the Born rule is the uniquely rational way of apportioning credence in Everettian quantum mechanics. In doing so, we rely on a single key principle: changes to the environment alone do not affect the probabilities one ought to assign to measurement outcomes in a local subsystem. We arrive at a method for assigning probabilities in cases that involve both classical and quantum self-locating uncertainty. This method provides unique answers to quantum Sleeping Beauty problems, as well as a well-defined procedure for calculating probabilities in quantum cosmological multiverses with multiple similar observers.

  • 1 Introduction
  • 2 Preliminaries: Many-Worlds, Self-locating Uncertainty, and Branch-counting
  •  2.1 The many-worlds interpretation
  •  2.2 Self-locating uncertainty and the Everettian multiverse
  •  2.3 Indifference and the quantitative probability problem
  •  2.4 Against branch-counting
  • 3 The Epistemic Irrelevance of the Environment
  •  3.1 The epistemic separability principle
  •  3.2 Deriving the Born rule
  • 4 Varieties of Uncertainty
  •  4.1 Epistemic separability principle and indifference
  •  4.2 Mixed uncertainties
  •  4.3 Large universe cosmology and the quantum multiverse
  • 5 Probability in Practice
  •  5.1 Betting and branching
  •  5.2 Theory confirmation
  • 6 Comparison to Other Approaches
  •  6.1 Zurek’s envariance-based derivation of the Born rule
  •  6.2 The decision-theoretic programme
  • 7 Conclusion
  • Appendix

Bell violation in the Sky. (arXiv:1607.00237v1 [hep-th])

quant-ph updates on arXiv.org

on 2016-7-04 7:42am GMT

Authors: Sayantan ChoudhurySudhakar PandaRajeev Singh

In this work, we have studied the possibility of setting up Bell’s inequality violating experiment in the context of cosmology, based on the basic principles of quantum mechanics. First we start with the physical motivation of implementing the Bell’s inequality violation in the context of cosmology. Then to set up the cosmological Bell violating test experiment we introduce a model independent theoretical framework using which we have studied the creation of new massive particles by implementing the WKB approximation method for the scalar fluctuations in presence of additional time dependent mass contribution. Next using the background scalar fluctuation in presence of new time dependent mass contribution, we explicitly compute the expression for the one point and two point correlation functions. Furthermore, using the results for one point function we introduce a new theoretical cosmological parameter which can be expressed in terms of the other known inflationary observables and can also be treated as a future theoretical probe to break the degeneracy amongst various models of inflation. Additionally, we also fix the scale of inflation in a model independent way without any prior knowledge of primordial gravitational waves. Next, we also comment on the technicalities of measurements from isospin breaking interactions and the future prospects of newly introduced massive particles in cosmological Bell violating test experiment. Further, we cite a precise example of this set up applicable in the context of string theory motivated axion monodromy model. Then we comment on the explicit role of decoherence effect and high spin on cosmological Bell violating test experiment. In fine, we provide a theoretical bound on the heavy particle mass parameter for scalar fields, graviton and other high spin fields from our proposed setup.

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Observation of the quantum paradox of separation of a single photon from one of its properties. (arXiv:1607.00302v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-04 7:42am GMT

Authors: James M. AshbyPeter D. SchwarzMaximilian Schlosshauer

We report an experimental realization of the quantum paradox of the separation of a single photon from one of its properties (the so-called “quantum Cheshire cat”). We use a modified Sagnac interferometer with displaced paths to produce appropriately pre- and postselected states of heralded single photons. Weak measurements of photon presence and circular polarization are performed in each arm of the interferometer by introducing weak absorbers and small polarization rotations and analyzing changes in the postselected signal. The absorber is found to have an appreciable effect only in one arm of the interferometer, while the polarization rotation significantly affects the signal only when performed in the other arm. We carry out both sequential and simultaneous weak measurements and find good agreement between measured and predicted weak values. In the language of Aharonov et al. and in the sense of the ensemble averages described by weak values, the experiment establishes the separation of a particle from one its properties during the passage through the interferometer.

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On the classical Schr\”odinger equation. (arXiv:1607.00168v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-04 7:42am GMT

Authors: Albert BensenyDavid TenaXavier Oriols

In this paper, the classical Schr\”odinger equation, which allows the study of classical dynamics in terms of wave functions, is analyzed theoretically and numerically. First, departing from classical (Newtonian) mechanics, and assuming an additional single-valued condition for the Hamilton’s principal function, the classical Schr\”odinger equation is obtained. This additional assumption implies inherent non-classical features on the description of the dynamics obtained from the classical Schr\”odinger equation: the trajectories do not cross in the configuration space. Second, departing from Bohmian mechanics and invoking the quantum-to-classical transition, the classical Schr\”odinger equation is obtained in a natural way for the center of mass of a quantum system with a large number of identical particles. This quantum development imposes the condition of dealing with a narrow wave packet, which implicitly avoids the non-classical features mentioned above. We illustrate all the above points with numerical simulations of the classical and quantum Schr\”odinger equations for different systems.

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Optimal uncertainty relations in a modified Heisenberg algebra. (arXiv:1607.00081v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-7-04 7:42am GMT

Authors: Kais AbdelkhalekWissam ChemissanyLeander FiedlerGianpiero ManganoRené Schwonnek

Various theories that aim at unifying gravity with quantum mechanics suggest modifications of the Heisenberg algebra for position and momentum. From the perspective of quantum mechanics, such modifications lead to new uncertainty relations which are thought (but not proven) to imply the existence of a minimal observable length. Here we prove this statement in a framework of sufficient physical and structural assumptions. Moreover, we present a general method that allows to formulate optimal and state-independent variance-based uncertainty relations. In addition, instead of variances, we make use of entropies as a measure of uncertainty and provide uncertainty relations in terms of min- and Shannon entropies. We compute the corresponding entropic minimal lengths and find that the minimal length in terms of min-entropy is exactly one bit.

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