Weekly Papers on Quantum Foundations (50)

This is a list of this week’s papers on quantum foundations published in various journals or uploaded to preprint servers such as arxiv.org and PhilSci Archive.

Quantum propagation across cosmological singularities. (arXiv:1612.02792v1 [gr-qc])

hep-th updates on arXiv.org

on 2016-12-10 7:33am GMT

Authors: Steffen GielenNeil Turok

The initial singularity is the most troubling feature of the standard cosmology, which quantum effects are hoped to resolve. In this paper, we study quantum cosmology with conformal (Weyl) invariant matter. We show it is natural to extend the scale factor to negative values, allowing a large, collapsing Universe to evolve across a quantum “bounce” into an expanding Universe like ours. We compute the Feynman propagator for Friedmann-Robertson-Walker backgrounds exactly, identifying curious pathologies in the case of curved (open or closed) universes. We then include anisotropies, fixing the operator ordering of the quantum Hamiltonian by imposing covariance under field redefinitions and again finding exact solutions. We show how complex classical solutions allow one to circumvent the singularity while maintaining the validity of the semiclassical approximation. The simplest isotropic universes sit on a critical boundary, beyond which there is qualitatively different behavior, with potential for instability. Additional scalars improve the theory’s stability. Finally, we study the semiclassical propagation of inhomogeneous perturbations about the flat, isotropic case, at linear and nonlinear order, showing that, at least at this level, there is no particle production across the bounce. These results form the basis for a promising new approach to quantum cosmology and the resolution of the big bang singularity.

The unspeakable why. (arXiv:1612.02680v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-12-10 7:32am GMT

Authors: Adán Cabello

For years, the biggest unspeakable in quantum theory has been why quantum theory and what is quantum theory telling us about the world. Recent efforts are unveiling a surprisingly simple answer. Here we show that two characteristic limits of quantum theory, the maximum violations of Clauser-Horne-Shimony-Holt and Klyachko-Can-Binicio\u{g}lu-Shumovsky inequalities, are enforced by a simple principle. The effectiveness of this principle suggests that non-realism is the key that explains why quantum theory.

Quantum jumps, superpositions, and the continuous evolution of quantum states

ScienceDirect Publication: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

on 2016-12-09 12:43pm GMT

Publication date: Available online 3 December 2016
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Rainer Dick
The apparent dichotomy between quantum jumps on the one hand, and continuous time evolution according to wave equations on the other hand, provided a challenge to Bohr’s proposal of quantum jumps in atoms. Furthermore, Schrödinger’s time-dependent equation also seemed to require a modification of the explanation for the origin of line spectra due to the apparent possibility of superpositions of energy eigenstates for different energy levels. Indeed, Schrödinger himself proposed a quantum beat mechanism for the generation of discrete line spectra from superpositions of eigenstates with different energies. However, these issues between old quantum theory and Schrödinger’s wave mechanics were correctly resolved only after the development and full implementation of photon quantization. The second quantized scattering matrix formalism reconciles quantum jumps with continuous time evolution through the identification of quantum jumps with transitions between different sectors of Fock space. The continuous evolution of quantum states is then recognized as a sum over continually evolving jump amplitudes between different sectors in Fock space. In today’s terminology, this suggests that linear combinations of scattering matrix elements are epistemic sums over ontic states. Insights from the resolution of the dichotomy between quantum jumps and continuous time evolution therefore hold important lessons for modern research both on interpretations of quantum mechanics and on the foundations of quantum computing. They demonstrate that discussions of interpretations of quantum theory necessarily need to take into account field quantization. They also demonstrate the limitations of the role of wave equations in quantum theory, and caution us that superpositions of quantum states for the formation of qubits may be more limited than usually expected.

Certified randomness in quantum physics

Nature – Issue – nature.com science feeds

on 2016-12-07 12:00am GMT

Certified randomness in quantum physics

Nature 540, 7632 (2016). doi:10.1038/nature20119

Authors: Antonio Acín & Lluis Masanes

The concept of randomness plays an important part in many disciplines. On the one hand, the question of whether random processes exist is fundamental for our understanding of nature. On the other, randomness is a resource for cryptography, algorithms and simulations. Standard methods for generating

Quantum physics: Photons in two colours at once

Nature – Issue – nature.com science feeds

on 2016-12-07 12:00am GMT

Quantum physics: Photons in two colours at once

Nature 540, 7632 (2016). doi:10.1038/540173d

Single light particles can be manipulated to form a mixture or ‘superposition’ of two colours at the same time.Quantum computing requires particles to be simultaneously in two quantum states, but the creation of two-colour photons requires individual light particles to interact, which they rarely

A new application of the modal-Hamiltonian interpretation of quantum mechanics: the problem of optical isomerism

Philsci-Archive: No conditions. Results ordered -Date Deposited.

on 2016-12-05 10:45pm GMT

Fortin, Sebastian and Lombardi, Olimpia and Martínez González, Juan Camilo (2016) A new application of the modal-Hamiltonian interpretation of quantum mechanics: the problem of optical isomerism. [Preprint]

Experimental Rectification of Entropy Production by Maxwell’s Demon in a Quantum System

PRL Editors’ Suggestions

on 2016-12-05 3:00pm GMT

Author(s): Patrice A. Camati, John P. S. Peterson, Tiago B. Batalhão, Kaonan Micadei, Alexandre M. Souza, Roberto S. Sarthour, Ivan S. Oliveira, and Roberto M. Serra

A new implementation of a Maxwell’s demon can control entropy production in a quantum-mechanical system that is driven out of thermal equilibrium.

[Phys. Rev. Lett. 117, 240502] Published Mon Dec 05, 2016

 

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