Weekly Papers on Quantum Foundations (26)

Author(s): Philippe Raynal

We consider quantum cellular automata on a body-centered cubic lattice and provide a simple derivation of the only two homogenous, local, isotropic, and unitary two-dimensional automata [G. M. D'Ariano and P. Perinotti,Phys. Rev. A 90, 062106 (2014)]. Our derivation relies on the notion of Gram mat...
[Phys. Rev. A 95, 062344] Published Fri Jun 30, 2017

Author(s): S. Ciliberto

Stochastic thermodynamics extends the traditional laws of thermodynamics to microscopic systems where thermal and quantum fluctuations cannot be ignored. This review summarizes progress in this field with a look at several experimental and theoretical results and a look toward potential applications in biology and nanotechnology.


[Phys. Rev. X 7, 021051] Published Fri Jun 30, 2017

Authors: Amaury Mouchet (LMPT)

Since its very beginnings, topology has forged strong links with physics and the last Nobel prize in physics, awarded in 2016 to Thouless, Haldane and Kosterlitz " for theoretical discoveries of topological phase transitions and topological phases of matter", confirmed that these connections have been maintained up to contemporary physics. To give some (very) selected illustrations of what is, and still will be, a cross fertilization between topology and physics, hydrodynamics provides a natural domain through the common theme offered by the notion of vortex, relevant both in classical (\S 2) and in quantum fluids (\S 3). Before getting into the details, I will sketch in \S 1 a general perspective from which this intertwining between topology and physics can be appreciated: the old dichotomy between discreteness and continuity, first dealing with antithetic thesis, eventually appears to be made of two complementary sides of a single coin.

Authors: Mateus AraújoPhilippe Allard GuérinÄmin Baumeler

One way to study the physical plausibility of closed timelike curves (CTCs) is to examine their computational power. This has been done for Deutschian CTCs (D-CTCs) and post-selection CTCs (P-CTCs), with the result that they allow for the efficient solution of problems in PSPACE and PP, respectively. Since these are extremely powerful complexity classes, which are not expected to be solvable in reality, this can be taken as evidence that these models for CTCs are pathological. This problem is closely related to the nonlinearity of this models, which also allows for example cloning quantum states, in the case of D-CTCs, or distinguishing non-orthogonal quantum states, in the case of P-CTCs. In contrast, the process matrix formalism allows one to model indefinite causal structures in a linear way, getting rid of these effects, and raising the possibility that its computational power is rather tame. In this paper we show that process matrices correspond to a linear particular case of P-CTCs, and therefore that its computational power is upperbounded by that of PP. We show, furthermore, a family of processes that can violate causal inequalities but nevertheless can be simulated by a causally ordered quantum circuit with only a constant overhead, showing that indefinite causality is not necessarily hard to simulate.

Afriat, Alexander (2017) Logic of gauge. [Preprint]
Mättig, Peter and Stoeltzner, Michael (2017) Model Choice and Crucial Tests. On the Empirical Epistemology of the Higgs Discovery. [Preprint]
McCoy, C.D. (2017) The implementation, interpretation, and justification of likelihoods in cosmology. [Preprint]
Eva, Benjamin and Hartmann, Stephan (2017) When No Reason For Is A Reason Against. [Preprint]
McCoy, C.D. (2017) An Objectivist’s Guide to Objective Chance. [Preprint]

Two-boson interference, a fundamentally quantum effect, has been extensively studied with photons through the Hong-Ou-Mandel effect and observed with guided plasmons. Using two freely propagating surface plasmon polaritons (SPPs) interfering on a lossy beam splitter, we show that the presence of loss enables us to modify the reflection and transmission factors of the beam splitter, thus revealing quantum interference paths that do not exist in a lossless configuration. We investigate the two-plasmon interference on beam splitters with different sets of reflection and transmission factors. Through coincidence-detection measurements, we observe either coalescence or anti-coalescence of SPPs. The results show that losses can be viewed as a degree of freedom to control quantum processes.

Publication date: Available online 27 June 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Vincent Ardourel
It is generally claimed that infinite idealizations are required for explaining phase transitions within statistical mechanics (e.g. Batterman 2011). Nevertheless, Menon and Callender (2013) have outlined theoretical approaches that describe phase transitions without using the infinite limit. This paper closely investigates one of these approaches, which consists of studying the complex zeros of the partition function (Borrmann et al., 2000). Based on this theory, I argue for the plausibility for eliminating the infinite limit for studying phase transitions. I offer a new account for phase transitions in finite systems, and I argue for the use of the infinite limit as an approximation for studying phase transitions in large systems.

Author(s): Cyril Elouard, David Herrera-Martí, Benjamin Huard, and Alexia Auffèves

The essence of both classical and quantum engines is to extract useful energy (work) from stochastic energy sources, e.g., thermal baths. In Maxwell’s demon engines, work extraction is assisted by a feedback control based on measurements performed by a demon, whose memory is erased at some nonzero e...
[Phys. Rev. Lett. 118, 260603] Published Thu Jun 29, 2017

Abstract

In this paper we examine some proposals to disprove the hypothesis that the interaction between mind and matter causes the collapse of the wave function, showing that such proposals are fundamentally flawed. We then describe a general experimental setup retaining the key features of the ones examined, and show that even a more general case is inadequate to disprove the mind-matter collapse hypothesis. Finally, we use our setup provided to argue that, under some reasonable assumptions about consciousness, such hypothesis is unfalsifiable.

Author(s): Robert B. Griffiths

The correctness of the consistent histories analysis of weakly interacting probes, related to the path of a particle, is maintained against the criticisms in the Comment, and against the alternative approach described there, which receives no support from standard (textbook) quantum mechanics.
[Phys. Rev. A 95, 066102] Published Wed Jun 28, 2017

Author(s): L. Vaidman

Griffiths [Phys. Rev. A 94, 032115 (2016)] analyzed, in the framework of a consistent histories interpretation, the controversy regarding the approach to the past of a quantum particle introduced by Vaidman [Phys. Rev. A87, 052104 (2013)]. I argue that Griffith's criticism of my approach using an a...
[Phys. Rev. A 95, 066101] Published Wed Jun 28, 2017

Logic-defying experiments in quantum causality can twist the notion of time itself.

Nature 546 590 doi: 10.1038/546590a

Authors: Yuri BonderChryssomalis ChryssomalakosDaniel Sudarsky

Any acceptable quantum gravity theory must allow us to recover the classical spacetime in the appropriate limit. Moreover, the spacetime geometrical notions should be intrinsically tied to the behavior of the matter that probes them. We consider some difficulties that would be confronted in attempting such an enterprise. The problems we uncover seem to go beyond the technical level to the point of questioning the overall feasibility of the project. The main issue is related to the fact that, in the quantum theory, it is impossible to assign a trajectory to a physical object, and, on the other hand, according to the basic tenets of the geometrization of gravity, it is precisely the trajectories of free localized objects that define the spacetime geometry. The insights gained in this analysis should be relevant to those interested in the quest for a quantum theory of gravity and might help refocus some of its goals.

Authors: Faramarz RahmaniMehdi Golshani

One of the important and famous topics in general theory of relativity and gravitation is the problem of geodesic deviation and its related singularity theorems. An interesting subject is the investigation of these concepts when quantum effects are considered. Since, the definition of trajectory is not possible in the framework of standard quantum mechanics (SQM), we investigate the problem of geodesic equation and its related topics in the framework of Bohmian quantum mechanics in which the definition of trajectory is possible. We do this in a fixed background and we do not consider the back-reaction effects of matter on the spacetime metric.

Abstract

It has been realized that the measurement problem of quantum mechanics is essentially the determinate-experience problem, and in order to solve the problem, the physical state representing the measurement result is required to be also the physical state on which the mental state of an observer supervenes. This necessitates a systematic analysis of the forms of psychophysical connection in the solutions to the measurement problem. In this paper, I propose a new, mentalistic formulation of the measurement problem which lays more stress on psychophysical connection. By this new formulation, it can be seen more clearly that the three main solutions to the measurement problem, namely Everett’s theory, Bohm’s theory and collapse theories, correspond to three different forms of psychophysical connection. I then analyze these forms of psychophysical connection. It is argued that the forms of psychophysical connection required by Everett’s and Bohm’s theories have potential problems, while an analysis of how the mental state of an observer supervenes on her wave function may help solve the structured tails problem of collapse theories.

Authors: Ovidiu Cristinel Stoica

Two thought experiments are analyzed, revealing that the quantum state of the universe does not contain definitive evidence of the wavefunction collapse. The first thought experiment shows that unitary quantum evolution alone can account for the outcomes of any combination of quantum experiments. This is in contradiction with the standard view on quantum measurement, which appeals to the wavefunction collapse, but it is in full agreement with the \emph{special state} proposal (L.S. Schulman, 1984, 1986, 1997) that there are some rare states that account for quantum experiments by unitary evolution alone. The second thought experiment consists in successive measurements, and reveals that the standard quantum measurement scheme predicts violations of the conservation laws. It is shown that the standard view on quantum measurements makes some unnecessary assumptions, which lead to the apparent necessity to invoke wavefunction collapse. Once these assumptions are removed, a new hope of a measurement scheme emerges, which, while still having open problems, it is compatible with both the unitary evolution and the conservation laws, and suggests means to experimentally distinguish between full unitarity and discontinuous collapse.

Myrvold, Wayne C. (2017) How Could Relativity be Anything Other Than Physical? [Preprint]
Brahma, Suddhasattwa (2017) Emergence of time in Loop Quantum Gravity. In: UNSPECIFIED.
Menon, Tushar (2017) Taking up superspace--what would it take to be a realist about superspace? In: UNSPECIFIED.

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