Weekly Papers on Quantum Foundations (27)

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.

Unconditional Quantum Correlations do not Violate Bell’s Inequality

Latest Results for Foundations of Physics

on 2015-7-04 12:00am GMT

Abstract

In this paper I demonstrate that the quantum correlations of polarization (or spin) observables used in Bell’s argument against local realism have to be interpreted as conditional quantum correlations. By taking into account additional sources of randomness in Bell’s type experiments, i.e., supplementary to source randomness, I calculate (in the standard quantum formalism) the complete quantum correlations. The main message of the quantum theory of measurement (due to von Neumann) is that complete correlations can be essentially smaller than the conditional ones. Additional sources of randomness diminish correlations. One can say another way around: transition from unconditional correlations to conditional can increase them essentially. This is true for both classical and quantum probability. The final remark is that classical conditional correlations do not satisfy Bell’s inequality. Thus we met the following conditional probability dilemma: either to use the conditional quantum probabilities, as was done by Bell and others, or complete quantum correlations. However, in the first case the corresponding classical conditional correlations need not satisfy Bell’s inequality and in the second case the complete quantum correlations satisfy Bell’s inequality. Thus in neither case we have a problem of mismatching of classical and quantum correlations. The whole structure of Bell’s argument was based on identification of conditional quantum correlations with unconditional classical correlations.

Potential Functions and the Characterization of Economics-Based Information

Latest Results for Foundations of Physics

on 2015-7-04 12:00am GMT

Abstract

The formulation of quantum mechanics as a diffusion process by Nelson (Phys Rev 150:1079–1085, 1966) provides for an interesting approach on how we may transit from classical mechanics into quantum mechanics. Besides the presence of the real potential function, another type of potential function (often denoted as ‘quantum potential’) forms an intrinsic part of this theory. In this paper we attempt to show how both types of potential functions can have a use in a resolutely macroscopic context like financial asset pricing. We are particularly interested in uncovering how the ‘quantum potential’ can add to the economics-based relevant information which is already supplied by the real potential function.

Quantum Information Biology: From Information Interpretation of Quantum Mechanics to Applications in Molecular Biology and Cognitive Psychology

Latest Results for Foundations of Physics

on 2015-7-04 12:00am GMT

Abstract

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. 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. 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.

Killing quantum entanglement by acceleration or a black hole. (arXiv:1507.00612v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-7-03 1:41am GMT

Authors: Yue DaiZhejun ShenYu Shi

We consider two entangled accelerating qubits coupled with real scalar fields, each described by the Unruh-Wald model. It is demonstrated that because of the Unruh effect, the bipartite entanglement of the two qubits suddenly dies when the acceleration of one or more qubits are large enough. We also consider three entangled accelerating qubits in GHZ state and in W state, with equal acceleration-frequency ratio, and found that in either state, the tripartite entanglement suddenly dies at a certain value of acceleration-frequency ratio. The equivalence between the Rindler metric and the Schwarzchild metric in the vicinity of the horizon of a black hole implies that for the two entangled qubits outside a black hole, the entanglement suddenly dies when one or both of the qubits are close enough to the horizon, while for the three entangled qubits in GHZ or W state, the tripartite entanglement suddenly dies when these qubits are close enough to the horizon.

AdS/CFT without holography: A hidden dimension on the CFT side and implications for black-hole entropy. (arXiv:1507.00591v1 [hep-th])

gr-qc updates on arXiv.org

on 2015-7-03 1:41am GMT

Authors: H. Nikolic

We propose a new non-holographic formulation of AdS/CFT correspondence, according to which quantum gravity on AdS and its dual non-gravitational field theory both live in the same number D of dimensions. The field theory, however, appears (D-1)-dimensional because the interactions do not propagate in one of the dimensions. The D-dimensional action for the field theory can be identified with the sum over (D-1)-dimensional actions with all possible values $\Lambda$ of the UV cutoff, so that the extra hidden dimension can be identified with $\Lambda$. Since there are no interactions in the extra dimension, most of the practical results of standard holographic AdS/CFT correspondence transcribe to non-holographic AdS/CFT without any changes. However, the implications on black-hole entropy change significantly. The maximal black-hole entropy now scales with volume, while the Bekenstein-Hawking entropy is interpreted as the minimal possible black-hole entropy. In this way, the non-holographic AdS/CFT correspondence offers a simple resolution of the black-hole information paradox, consistent with a recently proposed gravitational crystal.

Comment on Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics. (arXiv:1507.00544v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-7-03 1:41am GMT

Authors: Namit Anand

This is a comment to the paper, Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics by C Cisneros et al 1998 Eur. J. Phys. 19 237. doi:10.1088/0143-0807/19/3/005. The proof that the authors construct for the limitation on the superposition of state vectors corresponding to different sectors of the Hilbert space, partitioned by a superoperator has a flaw as outlined below.

Quantum communication in the presence of a horizon. (arXiv:1507.00402v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-7-03 1:41am GMT

Authors: Daiqin SuT.C. Ralph

Based on homodyne detection, we discuss how the presence of an event horizon affects quantum communication between an inertial partner, Alice, and a uniformly accelerated partner, Rob. We show that there exists a low frequency cutoff for Rob’s homodyne detector that maximizes the signal to noise ratio and it approximately corresponds to the Unruh frequency. In addition, the low frequency cutoff which minimizes the conditional variance between Alice’s input state and Rob’s output state is also approximately equal to the Unruh frequency. Thus the Unruh frequency provides a natural low frequency cutoff in order to optimize quantum communication of both classical and quantum information between Alice and Rob.

Dark matter, Mach’s ether and the QCD vacuum. (arXiv:1507.00460v1 [physics.hist-ph])

physics.hist-ph updates on arXiv.org

on 2015-7-03 1:41am GMT

Authors: Gilles Cohen-Tannoudji

Here is proposed the idea of linking the dark matter issue, (considered as a major problem of contemporary research in physics) with two other open theoretical questions, one, almost centenary about the existence of an unavoidable ether in general relativity agreeing with the Mach’s principle, and one more recent about the properties of the quantum vacuum of the quantum field theory of strong interactions, QuantumChromodynamics (QCD). According to this idea, on the one hand, dark matter and dark energy that, according to the current standard model of cosmology represent about 95% of the universe content, can be considered as two distinct forms of the Mach’s ether, and, on the other hand, dark matter, as a perfect fluid emerging from the QCD vacuum could be modeled as a Bose Einstein condensate.

Quantum gravito-optics: a light route from semiclassical gravity to quantum gravity

Classical and Quantum Gravity – latest papers

on 2015-7-02 12:00am GMT

Quantum gravity remains an elusive theory, in spite of our thorough understanding of the quantum theory and the general theory of relativity separately, presumably due to the lack of any observational clues. We argue that the theory of quantum gravity has a strong constraining anchor in the sector of gravitational radiation, ensuring reliable physical clues, albeit in a limited observable form. In particular, all types of gravitational waves expected to be observable in LIGO-like advanced detectors are fully quantum mechanical states of radiation. Exact equivalence of the full quantum gravity theory with the familiar semiclassical theory is ensured in the radiation sector, in most real situations where the relevant quantum operator functions are normal ordered, by the analogue of the optical equivalence theorem in quantum optics. We show that this is indeed the case for the detection of the waves from a massive binary system, a single gravitational atom, that emits coherent radia…

Quantum gravity: Draw the line

Nature Physics – Issue – nature.com science feeds

on 2015-7-01 12:00am GMT

Nature Physics 11, 523 (2015). doi:10.1038/nphys3400

Author: Iulia Georgescu

The Universe itself

Nature Physics – Issue – nature.com science feeds

on 2015-7-01 12:00am GMT

Nature Physics 11, 517 (2015). doi:10.1038/nphys3405

The general theory of relativity, tested time and time again, is a cornerstone of modern physics — but marrying it with quantum mechanics remains a major challenge.

Why I am not a QBist

Latest Results for Foundations of Physics

on 2015-7-01 12:00am GMT

Abstract

Quantum Bayesianism, or QBism, is a recent development of the epistemic view of quantum states, according to which the state vector represents knowledge about a quantum system, rather than the true state of the system. QBism explicitly adopts the subjective view of probability, wherein probability assignments express an agent’s personal degrees of belief about an event. QBists claim that most if not all conceptual problems of quantum mechanics vanish if we simply take a proper epistemic and probabilistic perspective. Although this judgement is largely subjective and logically consistent, I explain why I do not share it.

Superconducting transistors: A boost for quantum computing

Nature Physics – Issue – nature.com science feeds

on 2015-7-01 12:00am GMT

Nature Physics 11, 527 (2015). doi:10.1038/nphys3387

Author: Francesco Giazotto

A niobium titanite nitride-based superconducting nanodevice — a Cooper-pair transistor — has a remarkably long parity lifetime, exceeding one minute close to absolute zero.

Contextuality in Three Types of Quantum-Mechanical Systems

Latest Results for Foundations of Physics

on 2015-7-01 12:00am GMT

Abstract

We present a formal theory of contextuality for a set of random variables grouped into different subsets (contexts) corresponding to different, mutually incompatible conditions. Within each context the random variables are jointly distributed, but across different contexts they are stochastically unrelated. The theory of contextuality is based on the analysis of the extent to which some of these random variables can be viewed as preserving their identity across different contexts when one considers all possible joint distributions imposed on the entire set of the random variables. We illustrate the theory on three systems of traditional interest in quantum physics (and also in non-physical, e.g., behavioral studies). These are systems of the Klyachko–Can–Binicioglu–Shumovsky-type, Einstein–Podolsky–Rosen–Bell-type, and Suppes–Zanotti–Leggett–Garg-type. Listed in this order, each of them is formally a special case of the previous one. For each of them we derive necessary and sufficient conditions for contextuality while allowing for experimental errors and contextual biases or signaling. Based on the same principles that underly these derivations we also propose a measure for the degree of contextuality and compute it for the three systems in question.

Bell Inequalities, Experimental Protocols and Contextuality

Latest Results for Foundations of Physics

on 2015-7-01 12:00am GMT

Abstract

In this paper we give additional arguments in favor of the point of view that the violation of Bell, CHSH and CH inequalities is not due to a mysterious non locality of nature. We concentrate on an intimate relation between a protocol of a random experiment and a probabilistic model which is used to describe it. We discuss in a simple way differences between attributive joint probability distributions and generalized joint probability distributions of outcomes from distant experiments which depend on how the pairing of these outcomes is defined. We analyze in detail experimental protocols implied by local realistic and stochastic hidden variable models and show that they are incompatible with the protocols used in spin polarization correlation experiments. We discuss also the meaning of “free will”, differences between quantum and classical filters, contextuality of Kolmogorov models, contextuality of quantum theory (QT) and show how this contextuality has to be taken into account in probabilistic models trying to explain in an intuitive way the predictions of QT. The long range imperfect correlations between the clicks of distant detectors can be explained by partially preserved correlations between the signals created by a source. These correlations can only be preserved if the clicks are produced in a local and deterministic way depending on intrinsic parameters describing signals and measuring devices in the moment of the measurement. If an act of a measurement was irreducibly random they would be destroyed. It seems to indicate that QT may be in fact emerging from some underlying more detailed theory of physical phenomena. If this was a case then there is a chance to find in time series of experimental data some fine structures not predicted by QT. This would be a major discovery because it would not only prove that QT does not provide a complete description of individual physical systems but it would prove that it is not predictably complete.

CHSH Inequality: Quantum Probabilities as Classical Conditional Probabilities

Latest Results for Foundations of Physics

on 2015-7-01 12:00am GMT

Abstract

In this note we demonstrate that the results of observations in the EPR–Bohm–Bell experiment can be described within the classical probabilistic framework. However, the “quantum probabilities” have to be interpreted as conditional probabilities, where conditioning is with respect to fixed experimental settings. Our approach is based on the complete account of randomness involved in the experiment. The crucial point is that randomness of selections of experimental settings has to be taken into account within one consistent framework covering all events related to the experiment. This approach can be applied to any complex experiment in which statistical data are collected for various (in general incompatible) experimental settings.

Experimental Bounds on Classical Random Field Theories

Latest Results for Foundations of Physics

on 2015-7-01 12:00am GMT

Abstract

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 quantum mechanics alternatives which require power-dependent autocorrelation functions.

Dimensional reduction in causal set gravity. (arXiv:1506.08775v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-6-30 9:53am GMT

Authors: S. Carlip

Results from a number of different approaches to quantum gravity suggest that the effective dimension of spacetime may drop to $d=2$ at small scales. I show that two different dimensional estimators in causal set theory display the same behavior, and argue that a third, the spectral dimension, may exhibit a related phenomenon of “asymptotic silence.”

A new realization of quantum geometry. (arXiv:1506.08571v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-6-30 9:53am GMT

Authors: Benjamin BahrBianca DittrichMarc Geiller

We construct in this article a new realization of quantum geometry, which is obtained by quantizing the recently-introduced flux formulation of loop quantum gravity. In this framework, the vacuum is peaked on flat connections, and states are built upon it by creating local curvature excitations. The inner product induces a discrete topology on the gauge group, which turns out to be an essential ingredient for the construction of a continuum limit Hilbert space. This leads to a representation of the full holonomy-flux algebra of loop quantum gravity which is unitarily-inequivalent to the one based on the Ashtekar-Isham-Lewandowski vacuum. It therefore provides a new notion of quantum geometry. We discuss how the spectra of geometric operators, including holonomy and area operators, are affected by this new quantization. In particular, we find that the area operator is bounded, and that there are two different ways in which the Barbero-Immirzi parameter can be taken into account. The methods introduced in this work open up new possibilities for investigating further realizations of quantum geometry based on different vacua.

Time-dependant cosmological interpretation of quantum mechanics. (arXiv:1506.08299v1 [quant-ph])

gr-qc updates on arXiv.org

on 2015-6-30 9:53am GMT

Authors: Emmanuel Moulay (XLIM-SIC)

The aim of this article is to define a time-dependant cosmological interpretation of quantum mechanics in the context of a multiverse coming from eternal inflation. A common notion of time is defined for observers in similar observable universes by using the holographic principle. It is the time elapsed since the post-inflationary epoch. With this improvement, the cosmological interpretation of quantum mechanics becomes a full interpretation of quantum mechanics where the unitary evolution of quantum states is preserved. Moreover, it is well suited for eternal inflation .

Testing Wavefunction Collapse Models using Parametric Heating of a Trapped Nanosphere. (arXiv:1506.08782v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-6-30 9:53am GMT

Authors: Daniel GoldwaterMauro PaternostroP. F. Barker

We propose a mechanism for testing the theory of continuous spontaneous localization (CSL) by examining the parametric heating rate of a trapped nanosphere. The random localizations of the centre of mass for a given particle predicted by the CSL model can be modelled as a stochastic force embodying a source of heating for the nanosphere. We show that by utilising a Paul trap to levitate the particle coupled with optical cooling, it is possible to reduce environmental decoherence to such a level that CSL dominates the dynamics and contributes the main source of heating. We show that this approach allows measurements to be made on the timescale of seconds, and that the full parameter ranges given by Adler [J. Phys. A {\bf 40} 2935 (2006)] and Bassi [EPL {\bf 92} 5006 (2010)] ought to be testable using this scheme.

Quantum and classical areas of black hole thermodynamics. (arXiv:1506.08068v1 [gr-qc])

gr-qc updates on arXiv.org

on 2015-6-29 9:11am GMT

Authors: A. GhoshP. Mitra

Most calculations of black hole entropy in loop quantum gravity indicate a term proportional to the area eigenvalue A with a correction involving the logarithm of A. This violates the additivity of the entropy. An entropy proportional to A, with a correction term involving the logarithm of the classical area k, which is consistent with the additivity of entropy, is derived in both U(1) and SU(2) formulations.

The extraction of work from quantum coherence. (arXiv:1506.07875v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-6-29 9:11am GMT

Authors: Kamil KorzekwaMatteo LostaglioJonathan OppenheimDavid Jennings

We critically assess the problem of extracting work from a coherent superposition of energy eigenstates of an individual qubit system. By carefully taking into account all the resources involved in the thermodynamic transformations in a fully quantum-mechanical treatment, we show that there exists a thermal machine that can come arbitrarily close to extracting all the coherence as work. The machine only needs to act on individual copies of a state and can be reused. On the other hand, we show that for any thermal machine with finite resources not all the coherence of a state can be extracted as work. We provide explicit protocols extracting work from coherence when the resources of a thermal machine are bounded, a scenario potentially relevant for the thermodynamics at the nanoscale.

 

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