Weekly Papers on Quantum Foundations (20)

Laudisa, Federico (2017) Counterfactual Reasoning, Realism and Quantum Mechanics: Much Ado About Nothing? [Preprint]

Abstract

Based on a gambling formulation of quantum mechanics, we derive a Gleason-type theorem that holds for any dimension n of a quantum system, and in particular for \(n=2\) . The theorem states that the only logically consistent probability assignments are exactly the ones that are definable as the trace of the product of a projector and a density matrix operator. In addition, we detail the reason why dispersion-free probabilities are actually not valid, or rational, probabilities for quantum mechanics, and hence should be excluded from consideration.

Serafino, Loris (2017) The enigma of irreversibility and the interplay between Physics, Mathematics and Philosophy. [Preprint]

Zeno Hall Effect

  

on 2017-5-18 2:00pm GMT

Author(s): Zongping Gong, Sho Higashikawa, and Masahito Ueda

The quantum Zeno effect is predicted to give rise to Hall-effect-like behavior for wavepackets in an ultracold condensate.


[Phys. Rev. Lett. 118, 200401] Published Thu May 18, 2017

Kao, Molly (2017) Old Evidence in the Development of Quantum Theory. [Preprint]

Author(s): Felix Huber, Otfried Gühne, and Jens Siewert

Pure multiparticle quantum states are called absolutely maximally entangled if all reduced states obtained by tracing out at least half of the particles are maximally mixed. We provide a method to characterize these states for a general multiparticle system. With that, we prove that a seven-qubit st…
[Phys. Rev. Lett. 118, 200502] Published Wed May 17, 2017

Author(s): T. Ollikainen, K. Tiurev, A. Blinova, W. Lee, D. S. Hall, and M. Möttönen

Magnetic monopoles have been sought for decades but never definitively observed. Recent experiments have created different analogs of monopoles in Bose-Einstein condensates, including quantum-mechanical and Dirac monopoles. Now a new experiment in this system shows how a quantum-mechanical monopole can evolve into a Dirac monopole.


[Phys. Rev. X 7, 021023] Published Wed May 17, 2017

Author(s): Kiran E. Khosla and Natacha Altamirano

The notion of time is given a different footing in quantum mechanics and general relativity, treated as a parameter in the former and being an observer-dependent property in the latter. From an operational point of view time is simply the correlation between a system and a clock, where an idealized …
[Phys. Rev. A 95, 052116] Published Wed May 17, 2017

Atomic physics: Quantum theory verified by experiment

Nature 545, 7654 (2017). doi:10.1038/545293a

Authors: Ian B. Spielman

Systems of quantum objects can be characterized by the correlations between the objects. A technique that precisely measures even the most delicate of these correlations allows models of quantum systems to be tested. See Letter p.323

Hans Dehmelt (1922–2017)

Nature 545, 7654 (2017). doi:10.1038/545290a

Author: Peter Toschek

Nobel prizewinner who trapped electrons and demonstrated quantum jumps.

Abstract

The appearance of negative terms in quasiprobability representations of quantum theory is known to be inevitable, and, due to its equivalence with the onset of contextuality, of central interest in quantum computation and information. Until recently, however, nothing has been known about how much negativity is necessary in a quasiprobability representation. Zhu (Phys Rev Lett 117 (12):120404, 2016) proved that the upper and lower bounds with respect to one type of negativity measure are saturated by quasiprobability representations which are in one-to-one correspondence with the elusive symmetric informationally complete quantum measurements (SICs). We define a family of negativity measures which includes Zhu’s as a special case and consider another member of the family which we call “sum negativity.” We prove a sufficient condition for local maxima in sum negativity and find exact global maxima in dimensions 3 and 4. Notably, we find that Zhu’s result on the SICs does not generally extend to sum negativity, although the analogous result does hold in dimension 4. Finally, the Hoggar lines in dimension 8 make an appearance in a conjecture on sum negativity.

Authors: Juan Diaz DorronsoroJonathan J. HalliwellJames B. HartleThomas HertogOliver Janssen

It is shown that the standard no-boundary wave function has a natural expression in terms of a Lorentzian path integral with its contour defined by Picard-Lefschetz theory. The wave function is real, satisfies the Wheeler-DeWitt equation and predicts an ensemble of asymptotically classical, inflationary universes with nearly-Gaussian fluctuations and with a smooth semiclassical origin.

Authors: Tejinder P. Singh

We have recently proposed a new action principle for combining Einstein equations and the Dirac equation for a point mass. We used a length scale $L_{CS}$, dubbed the Compton-Schwarzschild length, to which the Compton wavelength and Schwarzschild radius are small mass and large mass approximations, respectively. Here we write down the field equations which follow from this action. We argue that the large mass limit yields Einstein equations, provided we assume wave function collapse and localisation for large masses. The small mass limit yields the Dirac equation. We explain why the Kerr-Newman black hole has the same gyromagnetic ratio as the Dirac electron, both being twice the classical value. The small mass limit also provides compelling reasons for introducing torsion, which is sourced by the spin density of the Dirac field. There is thus a symmetry between torsion and gravity: torsion couples to quantum objects through Planck’s constant $\hbar$ (but not $G$) and is important in the microscopic limit. Whereas gravity couples to classical matter, as usual, through Newton’s gravitational constant $G$ (but not $\hbar$), and is important in the macroscopic limit. We construct the Einstein-Cartan-Dirac equations which include the length $L_{CS}$. We find a potentially significant change in the coupling constant of the torsion driven cubic non-linear self-interaction term in the Dirac-Hehl-Datta equation. We speculate on the possibility that gravity is not a fundamental interaction, but emerges as a consequence of wave function collapse, and that the gravitational constant maybe expressible in terms of Planck’s constant and the parameters of dynamical collapse models.

Authors: Taro Kimura

We demonstrate how one can see quantization of geometry, and quantum algebraic structure in supersymmetric gauge theory.

Authors: Giovanni Amelino-CameliaGianluca CalcagniMichele Ronco

We here conjecture that two much-studied aspects of quantum gravity, dimensional flow and spacetime fuzziness, might be deeply connected. We illustrate the mechanism, providing first evidence in support of our conjecture, by working within the framework of multifractional theories, whose key assumption is an anomalous scaling of the spacetime dimension in the ultraviolet and a slow change of the dimension in the infrared. This sole ingredient is enough to produce a scale-dependent deformation of the integration measure with also a fuzzy spacetime structure. We also compare the multifractional correction to lengths with the types of Planckian uncertainty for distance and time measurements that was reported in studies combining quantum mechanics and general relativity heuristically. This allows us to fix two free parameters of the theory and leads, in one of the scenarios we contemplate, to a value of the ultraviolet dimension which had already found support in other quantum-gravity analyses. We also formalize a picture such that fuzziness originates from a fundamental discrete scale invariance at short scales and corresponds to a stochastic spacetime geometry, recovering the structure of Nottale scale relativity.

Authors: J. F. CariñenaJ. Clemente-GallardoJ.A. Jover-GaltierG. Marmo

A geometric description of the space of states of a finite-dimensional quantum system and of the Markovian evolution associated with the Kossakowski-Lindblad operator is presented. This geometric setting is based on two composition laws on the space of observables defined by a pair of contravariant tensor fields. The first one is a Poisson tensor field that encodes the commutator product and allows us to develop a Hamiltonian mechanics. The other tensor field is symmetric, encodes the Jordan product and provides the variances and covariances of measures associated with the observables. This tensorial formulation of quantum systems is able to describe, in a natural way, the Markovian dynamical evolution as a vector field on the space of states. Therefore, it is possible to consider dynamical effects on non-linear physical quantities, such as entropies, purity and concurrence. In particular, in this work the tensorial formulation is used to consider the dynamical evolution of the symmetric and skew-symmetric tensors and to read off the corresponding limits as giving rise to a contraction of the initial Jordan and Lie products.

Authors: Gábor HomaLajos Diósi

Solution of free particle quantum master equation with spatial decoherence can be unravelled into stochastic quantum trajectories in many ways. The first example, published in 1985, proposed a piecewise deterministic jump process for the wave function. While alternative unravellings, diffusive ones in particular, proved to be tractable analytically, the jump process 1985, also called orthojump, allows for few analytic results, it needs numeric methods as well. Here we prove that, similarly to diffusive unravellings, it is localizing the quantum state.

Quantum Weirdness

 Physics

on 2017-5-16 12:00am GMT

Author: William J. Mullin
ISBN: 9780198795131
Binding: Hardcover
Publication Date: 16 May 2017
Price: $39.95

Author(s): Fernando Pastawski and John Preskill

Deep theoretical links may exist between how space encodes information and error correcting codes being developed for quantum computers. A new analysis explores these connections further and offers insights into not just error-correction codes but also how we interpret ideas about spacetime.


[Phys. Rev. X 7, 021022] Published Mon May 15, 2017

Nature Physics. doi:10.1038/nphys4118

Authors: Yiqiu Ma, Haixing Miao, Belinda Heyun Pang, Matthew Evans, Chunnong Zhao, Jan Harms, Roman Schnabel & Yanbei Chen

Nature Physics. doi:10.1038/nphys4152

Author: Raffaele Flaminio

The Einstein–Podolsky–Rosen type of quantum entanglement can be used to improve the sensitivity of laser interferometer gravitational-wave detectors beyond the quantum limit.

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