Weekly Papers on Quantum Foundations (19)

Authors: M. A. Rajabpour

Under broad conditions, we prove that the probability amplitudes in the quantum mechanics are either always constant in time or changing continuously in any interval of time.

Authors: A. Martín-RuizC. A. Escobar

In this paper we investigate, within the standard model extension framework, the influence of Lorentz- and CPT-violating terms on gravitational quantum states of ultracold neutrons. Using a semiclassical wave packet, we derive the effective nonrelativistic Hamiltonian which describes the neutrons vertical motion by averaging the contributions from the perpendicular coordinates to the free falling axis. We compute the physical implications of the Lorentz- and CPT-violating terms on the spectra. The comparison of our results with those obtained in the GRANIT experiment leads to an upper bound for the symmetries-violation $c_{\mu\nu} ^{n}$ coefficients. We find that ultracold neutrons are sensitive to the $a _{i} ^{n}$ and $e _{i} ^{n}$ coefficients, which thus far are unbounded by experiments in the neutron sector. We propose two additional problems involving ultracold neutrons which could be relevant for improving our current bounds; namely, gravity-resonance-spectroscopy and neutron whispering gallery wave.

Authors: Tabish Qureshi (Centre for Theoretical Physics, JMI)

Two-slit interference experiment with a which-way detector has been a topic of intense debate. Scientific community is divided on the question whether the particle receives a momentum kick because of the process of which-way measurement. It is shown here that the same experiment can be viewed in two different ways, depending on which basis of the which-way detector states one chooses to look at. In one view, the loss of interference arises due to the entanglement of the two paths of the particle with two orthogonal states of the which-way detector. In another view, the loss of interference can be interpreted as arising from random momentum kicks of magnitude $h/2d$ received by the particle, $d$ being the slit separation. The same scenario is shown to hold for a three-slit interference experiment. The random momentum kicks for the three-slit case are of two kinds, of magnitude $\pm h/3d$. The two alternate views are described by the same quantum state, and hence are completely equivalent. The concept of “local” versus “nonlocal” kicks, much discussed in the literature, is not needed here.

Authors: Shahar Hod

Professor Jacob Bekenstein was known not only for his brilliant and original physical ideas, but also for their clear presentation in his lectures and seminal research papers. I here provide a short review of Bekenstein’s pioneering ideas about the quantization of black holes. I also describe my attempt, as a young and extremely naive student, to prove him wrong and how I got convinced in the correctness and utility of his deep physical intuition. Finally, my personal contribution to the ongoing attempts to understand the evenly spaced (discrete) area spectrum of quantized black holes, as originally suggested by Bekenstein in the early days of his scientific career, is described.

Authors: Carlo RovelliFrancesca Vidotto

We show that the expected lifetime of white holes formed as remnants of evaporated black holes is consistent with their production at reheating. We give a simple quantum description of these objects and argue that a quantum superposition of black and white holes with large interiors is stable, because it is protected by the existence of a minimal eigenvalue of the area, predicted by Loop Quantum Gravity. These two results support the hypothesis that a component of dark matter could be formed by small black hole remnants.

Publication date: Available online 27 April 2018
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Jeffrey Bub
In a recent result, Frauchiger & Renner argue that if quantum theory accurately describes complex systems like observers who perform measurements, then “we are forced to give up the view that there is one single reality.” Following a review of the Frauchiger-Renner argument, I argue that quantum mechanics should be understood probabilistically, as a new sort of non-Boolean probability theory, rather than representationally, as a theory about the elementary constituents of the physical world and how these elements evolve dynamically over time. I show that this way of understanding quantum mechanics is not in conflict with a consistent “single-world” interpretation of the theory.

Publication date: Available online 21 April 2018
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Niels S. Linnemann, Manus R. Visser
A possible way out of the conundrum of quantum gravity is the proposal that general relativity (GR) emerges from an underlying microscopic description. Despite recent interest in the emergent gravity program within the physics as well as the philosophy community, an assessment of the general motivation for this idea is lacking at the moment. We intend to fill this gap in the literature by discussing the main arguments in favour of the hypothesis that the metric field and its dynamics are emergent. First, we distinguish between microstructure inspired from GR, such as through quantization or discretization, and microstructure that is not directly motivated from GR, such as strings, quantum bits or condensed matter fields. The emergent gravity approach can then be defined as the view that the metric field and its dynamics are derivable from the latter type of microstructure. Subsequently, we assess in how far the following properties of (semi-classical) GR are suggestive of underlying microstructure: (1) the metric’s universal coupling to matter fields, (2) perturbative non-renormalizability, (3) black hole thermodynamics, and (4) the holographic principle. In the conclusion we formalize the general structure of the plausibility arguments put forward.

Publication date: 3 July 2018
Source:Physics Letters A, Volume 382, Issue 26
Author(s): Lawrence Horwitz, Rafael I. Arshansky
The relativistic quantum theory of Stueckelberg, Horwitz and Piron (SHP) describes in a simple way the experiment on interference in time of an electron emitted by femtosecond laser pulses carried out by Lindner et al. In this paper, we show that, in a way similar to our study of the Lindner et al. experiment (with some additional discussion of the covariant quantum mechanical description of spin and angular momentum), the experiment proposed by Palacios et al. to demonstrate entanglement of a two electron state, where the electrons are separated in time of emission, has a consistent interpretation in terms of the SHP theory. We find, after a simple calculation, results in essential agreement with those of Palacios et al.; but with the observed times as values of proper quantum observables.

NASA’s Cold Atom Laboratory will allow physicists to play with quantum phenomena like never before

— Read more on ScientificAmerican.com

      
Menon, Tushar (2018) Taking up superspace—the spacetime structure of supersymmetric field theory. [Preprint]
D’Ariano, Giacomo Mauro (2018) Causality re-established. [Preprint]
D’Ariano, Giacomo Mauro (2017) Physics Without Physics. [Preprint]
Fankhauser, Johannes (2017) Gravitational redshift, inertia, and the role of charge. [Preprint]

Author(s): Rafael Chaves, Gabriela Barreto Lemos, and Jacques Pienaar

Wave-particle duality has become one of the flagships of quantum mechanics. This counterintuitive concept is highlighted in a delayed-choice experiment, where the experimental setup that reveals either the particle or wave nature of a quantum system is decided after the system has entered the appara…
[Phys. Rev. Lett. 120, 190401] Published Mon May 07, 2018

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