Authors: Inge S. Helland

A general question is posed to the quantum community. Partial results are formulated in a self-contained way. In particular, the title question is answered affirmatorily in two cases: 1) The case of spin/ angular momentum of a partcle; 2) A general symmetry situation under certain technical assumptions.

Authors: Tamás Geszti

This is an extended discussion of Ref.[1], presenting a nonlinear dynamical model of quantum collapse, with randomness emerging from self-generated noise. Here we focus on a few issues: 1) the way chaos theory explains “deterministic but unpredictable” as a generic feature of nonlinear dynamics; 2) a new argument about why Bell-CHSH and GHZ experiments confirm quantum mechanics; 3) a discussion of why the heating effect predicted by CSL-type theories is not expected to happen according to our approach; 4) in looking for direct-product solutions of our nonlinear Von Neumann equation, we use a parametrization different from that used in Ref.[1], allowing better insight to the locality issue.

Authors: Yuri Ozhigov

Experimental attempts to implement quantum speedup of computations over the past 30 years have yielded a negative result, despite the absence of physical laws prohibiting such speedup. The article formulates the limitation of quantum formalism in the form of uncertainty “the complexity of the system – the accuracy of its description at the quantum level”, and provides arguments in favor of its physical status. An experiment to determine this constant through Grover’s algorithm is described. Rough estimates on the constant of this ratio are given, based on the possibility of applying the quantum theory to two processes: the emission of a photon by a Rubidium atom and the decay of an unstable isotope of Helium 6. This ratio explicitly prohibits the physical implementation of scalable fast quantum computations, but leaves the possibility of modeling the dynamics of real systems on a quantum computer, the only advantage of which is the use of quantum nonlocality.

Authors: Temple He, Matthew Headrick, Veronika E. Hubeny

We explore the structure of holographic entropy relations (associated with ‘information quantities’ given by a linear combination of entanglement entropies of spatial sub-partitions of a CFT state with geometric bulk dual). Such entropy relations can be recast in multiple ways, some of which have significant advantages. Motivated by the already-noted simplification of entropy relations when recast in terms of multipartite information, we explore additional simplifications when recast in a new basis, which we dub the K-basis, constructed from perfect tensor structures. For the fundamental information quantities such a recasting is surprisingly compact, in part due to the interesting fact that entropy vectors associated to perfect tensors are in fact extreme rays in the holographic entropy cone (as well as the full quantum entropy cone). More importantly, we prove that all holographic entropy inequalities have positive coefficients when expressed in the K-basis, underlying the key advantage over the entropy basis or the multipartite information basis.

Authors: Del Rajan (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)

The quantum Pusey–Barrett–Rudolph (PBR) theorem addresses the question of whether the quantum state corresponds to a $\psi$-ontic model (system’s physical state) or to a $\psi$-epistemic model (observer’s knowledge about the system). We reformulate the PBR theorem as a Monty Hall game, and show that winning probabilities, for switching doors in the game, depend whether it is a $\psi$-ontic or $\psi$-epistemic game. For certain cases of the latter, switching doors provides no advantage. We also apply the concepts involved to quantum teleportation, in particular for improving reliability.

Authors: James B. Hartle

In his essay “Nature Conformable to Herself” the late Murray Gell-Mann expands on an observation of Newton that theories of seemingly disparate phenomena in the universe often make use of similar ideas and similar mathematical structure. Newton summarized that by saying that nature was very consonant and conformable to herself. This essay uses a model of quantum cosmology to illustrate how, why, and when nature is conformable to herself.

Publication date: Available online 14 September 2019

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

Author(s): Patrick M. Duerr

Authors: Christopher Barton, Andrew Counsell, Fay Dowker, Dewi S. W. Gould, Ian Jubb, Gwylim Taylor

We propose a new definition of “horizon molecules” in Causal Set Theory following pioneering work by Dou and Sorkin. The new concept applies for any causal horizon and its intersection with any spacelike hypersurface. In the continuum limit, as the discreteness scale tends to zero, the leading behaviour of the expected number of horizon molecules is shown to be the area of the horizon in discreteness units, up to a dimension dependent factor of order one. We also determine the first order corrections to the continuum value, and show how such corrections can be exploited to obtain further geometrical information about the horizon and the spacelike hypersurface from the causal set.

Authors: S.Deser

Two simple, if Draconian, assumptions about classical gravity fix space-time’s dimension at D=4

Authors: Qingdi Wang

The cosmological constant problem is generated by very small scale quantum fields vacuum fluctuations. However, the standard formulation of the cosmological constant problem uses the very large scale (cosmological scale) homogeneous and isotropic FLRW metric to study the gravitational effect of these small scale vacuum fluctuations. This is problematic since at small scales both the spacetime metric and the quantum fields vacuum are wildly fluctuating and are highly inhomogeneous and anisotropic. By using a general fluctuating metric to describe these small scale fluctuations, we find that the cosmological constant problem does not arise since the large gravitational effect of the quantum vacuum is hided at small scale spacetime fluctuations. In addition, the stress energy tensor fluctuations of the quantum fields vacuum may serve as “dark energy” to drive the accelerating expansion of the Universe through a weak parametric resonance effect.

Author(s): M. D. Reid and Q. Y. He

Evidence for Bell’s nonlocality is so far mainly restricted to microscopic systems, where the elements of reality that are negated predetermine results of measurements to within one spin unit. Any observed nonlocal effect (or lack of classical predetermination) is then limited to no more than the di…

[Phys. Rev. Lett. 123, 120402] Published Fri Sep 20, 2019

Abstract

A recently popular formulation of the Higgs naturalness principle prohibits delicate cancellations between running renormalized Higgs mass parameters and EFT matching corrections, by contrast with the principle’s original formulation, which prohibits delicate cancellations between the bare Higgs mass parameter and its quantum corrections. While the need for this latter cancellation is sometimes viewed as unproblematic since bare parameters are thought by some to be divergent and unphysical, renormalized parameters are finite and measurable, and the need for delicate cancellations between the renormalized Higgs mass parameter and EFT matching corrections is therefore considered by some to constitute a more salient formulation of the Higgs naturalness problem. Here, we argue that to the contrary, the need for fine tuning of the renormalized Higgs mass parameter is an eliminable, unphysical artifact of renormalization scheme, and that this severely weakens the grounds for regarding it as a problematic instance of fine tuning. In doing so, we highlight what we take to be a number of important conceptual lessons about the physical interpretation of model parameters in QFT.

Boge, Florian (2019) Quantum information vs. epistemic logic: An analysis of the Frauchiger-Renner theorem. [Preprint]

Abstract

The contrast between the past-future symmetry of mechanical theories and the time-arrow observed in the behaviour of real complex systems doesn’t have nowadays a fully satisfactory explanation. If one confides in the Laplace-dream that everything be exactly and completely describable by the known mechanical differential equations, the whole experimental evidence of the irreversibility of real complex processes can only be interpreted as an illusion due to the limits of human brain and shortness of human history. In this work it is surmised that in the description of real events it would be more reasonable to renounce exactness and completeness of mechanical differential equations, assuming that also further effects exist in nature, governed by different kinds of rules, in spite of being so weak to be directly unobservable in single motions. This surmise can explain not only the time-arrow, but also why, in particular cases, it can happen that approximate and/or statistical models represent an improvement of mechanical theories instead of an approximation: this happened for Boltzmann gas-model and also for the famous work of Max Planck on blackbody-radiation. And it also appears as a more promising “working hypothesis”, stimulating and guiding us to learn more about limits and origin of the basic equations, and also about the nature of chance and the meaning of probability, which is nowadays not clear in spite of the fundamental role it plays in physics. Particularly that kind of probability which gives the connection between quantum–mechanical differential equations and observable events.

Author(s): Vasiliy Makhalov, Tanish Satoor, Alexandre Evrard, Thomas Chalopin, Raphael Lopes, and Sylvain Nascimbene

We report on an experimental study of the Lipkin-Meshkov-Glick model of quantum spins interacting at infinite range in a transverse magnetic field, which exhibits a ferromagnetic phase transition in the thermodynamic limit. We use dysprosium atoms of electronic spin J=8, subjected to a quadratic Zee…

[Phys. Rev. Lett. 123, 120601] Published Wed Sep 18, 2019

French, Steven (2019) Representation and Realism: On Being a Structuralist All the Way (Up and) Down. [Preprint]

Colanero, Klaus (2012) Decoherence and definite outcomes. [Preprint]

Dethier, Corey (2019) Forces in A True and Physical Sense: From Mathematical Models to Metaphysical Conclusions. [Preprint]