Weekly Papers on Quantum Foundations (2)

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.

Multipartite Bell-type inequality by generalizing Wigner’s argument

PRA: Fundamental concepts

on 2015-1-09 3:00pm GMT

Author(s): Dipankar Home, Debashis Saha, and Siddhartha Das

Wigner’s argument inferring a Bell-type inequality for the Einstein–Podolsky–Rosen–Bohm entangled state is generalized here for any N-partite state. This is based on assuming for the relevant dichotomic observables the existence of the overall joint probability distributions, satisfying the locality…

[Phys. Rev. A 91, 012102] Published Fri Jan 09, 2015

A unified formulation for entanglement of distinguishable and indistinguishable particles. (arXiv:1501.01743v1 [quant-ph])

quant-ph updates on arXiv.org

on 2015-1-09 1:47am GMT

Authors: Swapnamay Mondal

Entanglement is a well understood concept only for distinguishable particles. However fundamental particles being inherently indistinguishable, it is desirable to have a single formulation for entanglement of distinguishable and indistinguishable particles. We take such a unified notion to be defined in connection with a measurement whose outcome gives R\`{e}nyi entropies when two subsystems are perfectly distinguishable, and which remains well defined even when two subsystems can not be distinguished perfectly. An explicit formula for outcome of such a measurement, which we call “exact R\`{e}nyi entropy”, is conjectured in terms of “normalized” R\'{e}nyi entropies of spatial regions in field theory. Same idea is used to define “exact Von Neumann entropy” as well. Our formula works for both statistics and to leading order reproduces R\'{e}nyi/Von Neumann entropies of distinguishable particles. Corrections due to indistinguishability are finite in number, they depend on spatial overlap of the wave functions and are not invariant under local unitaries and also sensitive to dynamics of the system. It is argued that in a generic situation no finite dimensional density matrix can account for all these R\'{e}nyi entropies. These results provide some insight into how quantum mechanics emerges from quantum field theory in the context of entanglement. Our formula is experimentally verifiable and we point out some qualitative features of our formula that are relatively easy to verify experimentally.

Uncertainty relation in Schwarzschild spacetime. (arXiv:1501.01700v1 [hep-th])

quant-ph updates on arXiv.org

on 2015-1-09 1:47am GMT

Authors: Jun FengYao-Zhong ZhangMark D. GouldHeng Fan

We explore the entropic uncertainty relation in the curved background outside a Schwarzschild black hole, and find that Hawking radiation introduce a nontrivial modification on the uncertainty bound for particular observer, therefore could be witnessed by proper uncertainty game experimentally. We first investigate an uncertainty game between a free falling observer and his static partner holding a quantum memory initially entangled with the quantum system to be measured. Due to the information loss from Hawking decoherence, we find an inevitably increase of the uncertainty on the outcome of measurements in the view of static observer, which is dependent on the mass of the black hole, the distance of observer from event horizon, and the mode frequency of quantum memory. In an alternative game between two static players, we show that quantum information of qubit can be transferred to quantum memory through a bath of fluctuating quantum fields outside the black hole, which triggers an effectively reduced uncertainty bound that violate the intrinsic limit $-\log_2c$. Numerically estimation for a proper choice of initial state shows that the analysis is comparable with possible real experiments. Moreover, the relation between our results and other uncertainty probe, e.g., time-energy uncertainty, is also discussed.

Condensed Matter Lessons About the Origin of Time

Latest Results for Foundations of Physics

on 2015-1-08 12:00am GMT

Abstract

It is widely hoped that quantum gravity will shed light on the question of the origin of time in physics. The currently dominant approaches to a candidate quantum theory of gravity have naturally evolved from general relativity, on the one hand, and from particle physics, on the other hand. A third important branch of twentieth century ‘fundamental’ physics, condensed-matter physics, also offers an interesting perspective on quantum gravity, and thereby on the problem of time. The bottomline might sound disappointing: to understand the origin of time, much more experimental input is needed than what is available today. Moreover it is far from obvious that we will ever find out the true origin of physical time, even if we become able to directly probe physics at the Planck scale. But we might learn some interesting lessons about time and the structure of our universe in the process. A first lesson is that there are probably several characteristic scales associated with “quantum gravity” effects, rather than the single Planck scale usually considered. These can differ by several orders of magnitude, and thereby conspire to hide certain effects expected from quantum gravity, rendering them undetectable even with Planck-scale experiments. A more tentative conclusion is that the hierarchy between general relativity, special relativity and Newtonian physics, usually taken for granted, might have to be interpreted with caution.

Fundamental physical ontologies and the constraint of empirical coherence: a defense of wave function realism

Latest Results for Synthese

on 2015-1-07 12:00am GMT

Abstract

This paper defends wave function realism against the charge that the view is empirically incoherent because our evidence for quantum theory involves facts about objects in three-dimensional space or space-time (local beables). It also criticizes previous attempts to defend wave function realism against this charge by claiming that the wave function is capable of grounding local beables as elements of a derivative ontology.

Many worlds: decoherent or incoherent?

Latest Results for Synthese

on 2015-1-07 12:00am GMT

Abstract

We claim that, as it stands, the Deutsch–Wallace–Everett approach to quantum theory is conceptually incoherent. This charge is based upon the approach’s reliance upon decoherence arguments that conflict with its own fundamental precepts regarding probabilistic reasoning in two respects. This conceptual conflict obtains even if the decoherence arguments deployed are aimed merely towards the establishment of certain ‘emergent’ or ‘robust’ structures within the wave function: To be relevant to physical science notions such as robustness must be empirically grounded, and, on our analysis, this grounding can only plausibly be done in precisely the probabilistic terms that lead to conceptual conflict. Thus, the incoherence problems presented necessitate either the provision of a new, non-probabilistic empirical grounding for the notions of robustness and emergence in the context of decoherence, or the abandonment of the Deutsch–Wallace–Everett programme for quantum theory.

Mutual information as an order parameter for quantum synchronization

PRA: Quantum information

on 2015-1-05 3:00pm GMT

Author(s): V. Ameri, M. Eghbali-Arani, A. Mari, A. Farace, F. Kheirandish, V. Giovannetti, and R. Fazio

Spontaneous synchronization is a fundamental phenomenon, important in many theoretical studies and applications. Recently, this effect has been analyzed and observed in a number of physical systems close to the quantum-mechanical regime. In this work we propose mutual information as a useful order p…

[Phys. Rev. A 91, 012301] Published Mon Jan 05, 2015

Quantum mechanics: No more fields

Nature Physics – AOP – nature.com science feeds

on 2015-1-05 12:00am GMT

Nature Physics. doi:10.1038/nphys3226

Author: Maciej Lewenstein

A self-accelerating electronic wave packet can acquire a phase akin to the Aharonov–Bohm effect, but in the absence of a magnetic field.

Quantum shells in a quantum space-time

Classical and Quantum Gravity – latest papers

on 2015-1-05 12:00am GMT

We study the quantum motion of null shells in the quantum space-time of a black hole in loop quantum gravity. We treat the shells as test fields and use an effective dynamics for the propagation equations. The shells propagate through the region where the singularity was present in the classical black hole space-time, but is absent in the quantum space-time, eventually emerging through a white hole to a new asymptotic region of the quantum space-time. The profiles of the shells get distorted due to the quantum fluctuations in the Planckian region that replaces the singularity. The evolution of the shells is unitary throughout the whole process.

 

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