Weekly Papers on Quantum Foundations (10)

Authors: Erhard Scholz

Weyl's original scale geometry of 1918 ("purely infinitesimal geometry") was withdrawn by its author from physical theorizing in the early 1920s. It had a comeback in the last third of the 20th century in different contexts: scalar tensor theories of gravity, foundations of gravity, foundations of quantum mechanics, elementary particle physics, and cosmology. It seems that Weyl geometry continues to offer an open research potential for the foundations of physics even after the turn to the new millennium.

Authors: Steven B. Giddings

Quantum modifications to black holes on scales comparable to the horizon size, or even more radical physics, are apparently needed to reconcile the existence of black holes with the principles of quantum mechanics. This piece gives an overview of some possible observational tests for such departures from a classical description of black holes, via gravitational wave detection and very long baseline interferometry. (Invited comment for Nature Astronomy.)

Authors: Q. DupreyS. KanjilalU. SinhaD. HomeA. Matzkin

The Quantum Cheshire Cat [New J. Phys. 15, 113015, 2013] (QCC) is an effect defined within the Weak Measurements framework by which a property of a quantum particle appears to be spatially separated from its position. The status of this effect has however remained unclear, as claims of experimental observation of the QCC have been disputed by strong criticism of the experimental as well as the theoretical aspects of the effect. In this paper we clarify in what precise sense the QCC can be regarded as an unambiguous consequence of the standard quantum mechanical formalism applied to describe quantum pointers weakly coupled to a system. In light of this clarification, the raised criticisms of the QCC effect are rebutted. We further point out that the limitations of the experiments performed to date imply that a loophole-free experimental demonstration of the QCC has not yet been achieved.

Authors: Zichang HeWen Jiang

Categorization is necessary for many decision making tasks. However, the categorization process may interfere the decision making result and the law of total probability can be violated in some situations. To predict the interference effect of categorization, some model based on quantum probability has been proposed. In this paper, a new quantum dynamic belief (QDB) model is proposed. Considering the precise decision may not be made during the process, the concept of uncertainty is introduced in our model to simulate real human thinking process. Then the interference effect categorization can be predicted by handling the uncertain information. The proposed model is applied to a categorization decision-making experiment to explain the interference effect of categorization. Compared with other models, our model is relatively more succinct and the result shows the correctness and effectiveness of our model.

Author(s): Michael Zwolak and Wojciech H. Zurek

The objective, classical world emerges from the underlying quantum substrate via the proliferation of redundant copies of selected information into the environment, which acts as a communication channel, transmitting that information to observers. These copies are independently accessible, allowing …
[Phys. Rev. A 95, 030101(R)] Published Wed Mar 08, 2017

Publication date: 18 April 2017
Source:Physics Letters A, Volume 381, Issue 15
Author(s): Mariami Gachechiladze, Otfried Gühne
In a paper by Popescu and Rohrlich [1] a proof has been presented showing that any pure entangled multiparticle quantum state violates some Bell inequality. We point out a gap in this proof, but we also give a construction to close this gap. It turns out that with some extra effort all the results from the aforementioned publication can be proven. Our construction shows how two-particle entanglement can be generated via performing local projections on a multiparticle state.

Authors: William G. UnruhRobert M. Wald

The complete gravitational collapse of a body in general relativity will result in the formation of a black hole. Although the black hole is classically stable, quantum particle creation processes will result in the emission of Hawking radiation to infinity and corresponding mass loss of the black hole, eventually resulting in the complete evaporation of the black hole. Semiclassical arguments strongly suggest that, in the process of black hole formation and evaporation, a pure quantum state will evolve to a mixed state, i.e., there will be "information loss." There has been considerable controversy over this issue for more than 40 years. In this review, we present the arguments in favor of information loss, and analyze some of the counter-arguments and alternative possibilities.

Authors: Job FeldbruggeJean-Luc LehnersNeil Turok

We argue that the Lorentzian path integral is a better starting point for quantum cosmology than the Euclidean version. In particular, we revisit the mini-superspace calculation of the Feynman path integral for quantum gravity with a positive cosmological constant. Instead of rotating to Euclidean time, we deform the contour of integration over metrics into the complex plane, exploiting Picard-Lefschetz theory to transform the path integral from a conditionally convergent integral into an absolutely convergent one. We show that this procedure unambiguously determines which semiclassical saddle point solutions are relevant to the quantum mechanical amplitude. Imposing "no-boundary" initial conditions, i.e., restricting attention to regular, complex metrics with no initial boundary, we find that the dominant saddle contributes a semiclassical exponential factor which is precisely the {\it inverse} of the famous Hartle-Hawking result.

Authors: Alain Connes

We give a survey of our joint ongoing work with Ali Chamseddine, Slava Mukhanov and Walter van Suijlekom. We show how a problem purely motivated by "how geometry emerges from the quantum formalism" gives rise to a slightly noncommutative structure and a spectral model of gravity coupled with matter which fits with experimental knowledge. This text will appear as a contribution to the volume: "Foundations of Mathematics and Physics one century after Hilbert". Editor: Joseph Kouneiher. Collection Mathematical Physics, Springer 2017


Quantum violation of Bell inequalities is now used in many quantum information applications and it is important to analyze it both quantitatively and conceptually. In the present paper, we analyze violation of multipartite Bell inequalities via the local probability model—the LqHV (local quasi hidden variable) model (Loubenets in J Math Phys 53:022201, 2012), incorporating the LHV model only as a particular case and correctly reproducing the probabilistic description of every quantum correlation scenario, more generally, every nonsignaling scenario. The LqHV probability framework allows us to construct nonsignaling analogs of Bell inequalities and to specify parameters quantifying violation of Bell inequalities—Bell’s nonlocality—in a general nonsignaling case. For quantum correlation scenarios on an N-qudit state, we evaluate these nonlocality parameters analytically in terms of dilation characteristics of an N-qudit state and also, numerically—in d and N. In view of our rigorous mathematical description of Bell’s nonlocality in a general nonsignaling case via the local probability model, we argue that violation of Bell inequalities in a quantum case is not due to violation of the Einstein–Podolsky–Rosen (EPR) locality conjectured by Bell but due to the improper HV modelling of “quantum realism”.

Hoehn, Philipp A (2017) Quantum theory from rules on information acquisition. In: UNSPECIFIED.
Christian, Joy (2017) Refutation of Richard Gill's Argument Against my Disproof of Bell's Theorem. [Preprint]

de Sitter Space as a Resonance


on 2017-3-07 3:00pm GMT

Author(s): Jonathan Maltz and Leonard Susskind

de Sitter space is shown to arise as resonance in transition amplitudes in quantum gravity.

[Phys. Rev. Lett. 118, 101602] Published Tue Mar 07, 2017

Authors: D. Sokolovski

The Salecker-Wigner-Peres (SWP) clock is often used to determine the duration a quantum particle is supposed to spend is a specified region of space $\Om$. By construction, the result is a real positive number, and the method seems to avoid the difficulty of introducing complex time parameters, which arises in the Feynman paths approach. However, it tells very little about what is being learnt about the particle's motion. We investigate this matter further, and show that the SWP clock, like any other Larmor clock, correlates the rotation of its angular momentum with the durations $\tau$ Feynman paths spend in $\Om$, therefore destroying interference between different durations. An inaccurate weakly coupled clock leaves the interference almost intact, and the need to resolve resulting "which way?" problem is the main difficulty at the centre of the "tunnelling time" controversy. In the absence of a probability distribution for the values of $\tau$, the SWP results are expressed in terms of moduli of the "complex times", given by the weighted sums of the corresponding probability amplitudes. It is shown that over-interpretation of these results, by treating the SWP times as physical time intervals, leads to paradoxes and should be avoided. We analyse various settings of the SWP clock, different calibration procedures, and the relation between the SWP results and the quantum dwell time. Our general analysis is applied to the cases of stationary tunnelling and tunnel ionisation

Authors: Ralf BlattmannKlaus Mølmer

We study the fluctuations of the work performed on a driven quantum system, defined as the difference between subsequent measurements of energy eigenvalues. These work fluctuations are governed by statistical theorems with similar expressions in classical and quantum physics. In this article we show that we can distinguish quantum and classical work fluctuations, as the latter can be described by a macrorealistic theory and hence obey Leggett-Garg inequalities. We show that these inequalities are violated by quantum processes in a driven two-level system and in a harmonic oscillator subject to a squeezing transformation.

Authors: Ian T. Durham

According to quantum theory, randomness is a fundamental property of the universe yet classical physics is mostly deterministic. In this article I show that it is possible for deterministic systems to arise from random ones and discuss the implications of this for the concept of free will.

Tappenden, Paul (2017) Objective Probability and the Mind-Body Relation. [Preprint]
Myrvold, Wayne C. and Albert, David Z. and Callender, Craig and Ismael, Jenann (2016) Book Symposium: David Albert, After Physics. UNSPECIFIED.

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