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.

Measurement and Fundamental Processes in Quantum Mechanics

Latest Results for Foundations of Physics

on 2015-4-04 12:00am GMT

Abstract

In the standard mathematical formulation of quantum mechanics, measurement is an additional, exceptional fundamental process rather than an often complex, but ordinary process which happens also to serve a particular epistemic function: during a measurement of one of its properties which is not already determined by a preceding measurement, a measured system, even if closed, is taken to change its state discontinuously rather than continuously as is usual. Many, including Bell, have been concerned about the fundamental role thus given to measurement in the foundation of the theory. Others, including the early Bohr and Schwinger, have suggested that quantum mechanics naturally incorporates the unavoidable uncontrollable disturbance of physical state that accompanies any local measurement without the need for an exceptional fundamental process or a special measurement theory. Disturbance is unanalyzable for Bohr, but for Schwinger it is due to physical interactions’ being borne by fundamental particles having discrete properties and behavior which is beyond physical control. Here, Schwinger’s approach is distinguished from more well known treatments of measurement, with the conclusion that, unlike most, it does not suffer under Bell’s critique of quantum measurement. Finally, Schwinger’s critique of measurement theory is explicated as a call for a deeper investigation of measurement processes that requires the use of a theory of quantum fields.

Atomic Hong–Ou–Mandel experiment

Nature - Issue - nature.com science feeds

on 2015-4-03 12:57am GMT

**Atomic Hong–Ou–Mandel experiment**

Nature 520, 7545 (2015). doi:10.1038/nature14331

Authors: R. Lopes, A. Imanaliev, A. Aspect, M. Cheneau, D. Boiron & C. I. Westbrook

Two-particle interference is a fundamental feature of quantum mechanics, and is even less intuitive than wave–particle duality for a single particle. In this duality, classical concepts—wave or particle—are still referred to, and interference happens in ordinary space-time. On the other hand, two-particle interference takes place

Emergent Spacetime: Reality or Illusion?. (arXiv:1504.00464v1 [hep-th])

on 2015-4-03 12:54am GMT

Authors: Hyun Seok Yang

The contemporary physics has revealed growing evidences that the emergence can be applied to not only biology and condensed matter systems but also gravity and spacetime. We observe that noncommutative spacetime necessarily implies emergent spacetime if spacetime at microscopic scales should be viewed as noncommutative. Since the emergent spacetime is a new fundamental paradigm for quantum gravity, it is necessary to reexamine all the rationales to introduce the multiverse hypothesis from the standpoint of emergent spacetime. We argue that the emergent spacetime certainly opens a new perspective that may cripple all the rationales to introduce the multiverse picture. Moreover the emergent spacetime may rescue us from the doomsday of metastable multiverse as quantum mechanics did from the catastrophic collapse of classical atoms.

Bohm's quantum potential as an internal energy

ScienceDirect Publication: Physics Letters A

on 2015-4-02 6:50pm GMT

Publication date: 26 June 2015

**Source:**Physics Letters A, Volume 379, Issues 18–19

Author(s): Glen Dennis , Maurice A. de Gosson , Basil J. Hiley

We pursue our discussion of Fermi's surface initiated by Dennis, de Gosson and Hiley and show that Bohm's quantum potential can be viewed as an internal energy of a quantum system, giving further insight into its role in stationary states. This implies that the ‘particle’ referred to in Bohm's theory is not a classical point-like object but rather has an extended structure in phase space which can be linked to the notion of a symplectic capacity, a topological feature of the underlying symplectic geometry. This structure provides us with a new, physically motivated derivation of Schrödinger's equation provided we interpret Gleason's theorem as a derivation of the Born rule from fundamental assumptions about quantum probabilities.

Quantum Coherence, Time-Translation Symmetry, and Thermodynamics

Recent Articles in Phys. Rev. X

on 2015-4-01 2:00pm GMT

Author(s): Matteo Lostaglio, Kamil Korzekwa, David Jennings, and Terry Rudolph

Quantum mechanics and thermodynamics are fundamental fields of physics. Scientists show how the processing of quantum coherence is constrained by the laws of thermodynamics.

[Phys. Rev. X 5, 021001] Published Wed Apr 01, 2015

T Violation and the Unidirectionality of Time: Further Details of the Interference

Latest Results for Foundations of Physics

on 2015-3-31 12:00am GMT

Abstract

T violation has previously been shown to induce destructive interference between different paths that the universe can take through time which leads to a new quantum equation of motion called bievolution. Here we examine further details of the interference and clarify the conditions needed for the bievolution equation.

Quantum origins of objectivity

on 2015-3-30 2:00pm GMT

Author(s): R. Horodecki, J. K. Korbicz, and P. Horodecki

In spite of all of its successes, quantum mechanics leaves us with a central problem: How does nature create a bridge from fragile quanta to the objective world of everyday experience? Here we find that a basic structure within quantum mechanics that leads to the perceived objectivity is a so-called...

[Phys. Rev. A 91, 032122] Published Mon Mar 30, 2015

on 2015-3-30 4:00am GMT

Authors: K. A. Milton

Starting from the earlier notions of stationary action principles, we show how Julian Schwinger's Quantum Action Principle descended from Dirac's formulation, which independently led Feynman to his path-integral formulation of quantum mechanics. The connection between the two is brought out, and applications are discussed. The Keldysh-Schwinger time-cycle method of extracting matrix elements in nonequilibrium situations is described. The variational formulation of quantum field theory and the development of source theory constitute the latter part of this work. In this document, derived from Schwinger's lectures over four decades, the continuity of concepts, such as that of Green's functions, becomes apparent.

Unconditional quantum correlations do not violate Bell's inequality. (arXiv:1503.08016v1 [quant-ph])

on 2015-3-30 4:00am GMT

Authors: Andrei Khrennikov

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 {\it 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 {\it 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. It seems that the whole structure of Bell's argument was based on unacceptable identification of conditional quantum correlations with unconditional classical correlations.

Riding Gravity Away from Doomsday. (arXiv:1503.08130v1 [hep-th])

on 2015-3-30 3:59am GMT

Authors: Ashoke Sen

The discovery that most of the energy density in the universe is stored in the form of dark energy has profound consequences for our future. In particular our current limited understanding of quantum theory of gravity indicates that some time in the future our universe will undergo a phase transition that will destroy us and everything else around us instantaneously. However the laws of gravity also suggest a way out -- some of our descendants could survive this catastrophe by riding gravity away from the danger. In this essay I describe the tale of this escape from doomsday.

Cosmological Collider Physics. (arXiv:1503.08043v1 [hep-th])

on 2015-3-30 3:59am GMT

Authors: Nima Arkani-Hamed, Juan Maldacena

We study the imprint of new particles on the primordial cosmological fluctuations. New particles with masses comparable to the Hubble scale produce a distinctive signature on the non-gaussianities. This feature arises in the squeezed limit of the correlation functions of primordial fluctuations. It consists of particular power law, or oscillatory, behavior that contains information about the masses of new particles. There is an angular dependence that gives information about the spin. We also have a relative phase that crucially depends on the quantum mechanical nature of the fluctuations and can be viewed as arising from the interference between two processes. While some of these features were noted before in the context of specific inflationary scenarios, here we give a general description emphasizing the role of symmetries in determining the final result.

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