Weekly Papers on Quantum Foundations (14)

Accessing inaccessible information via quantum indistinguishability. (arXiv:2203.16592v1 [quant-ph])

上午9:20

Sebastian Horvat, Borivoje Dakić

quant-ph updates on arXiv.org

Suppose that Alice stumbles upon a box containing some confidential information and wishes to read out the latter. The problem is that the box is practically unbreakable and the information is so encoded as not to leave any physical trace in the environment, thereby leaving Alice with apparently no means of gathering the information. While the information is per assumption inaccessible classically, we show that it can be read out almost perfectly within quantum mechanics. Interestingly, the task can be accomplished only if Alice employs additional boxes, which need to be identical to the initial one in the quantum-mechanical sense. After formalizing the task we show how its solution relies on an interplay between entanglement and quantum indistinguishability. We also discuss the broader merit of our findings, thereby pointing out their relevance for quantum information processing.

We cannot believe we overlooked these Majorana discoveries. (arXiv:2203.17060v1 [cond-mat.mes-hall])

上午9:20

Sergey Frolov, Vincent Mourik

quant-ph updates on arXiv.org

In 2011-2012 we performed experiments on hybrid superconductor-semiconductor nanowire devices which yielded signatures of Majorana fermions based on zero-bias peaks in tunneling measurements. The research field that grew out of those findings and other contemporary works has advanced significantly, and a lot of new knowledge and insights were gained. However, key smoking gun evidence of Majorana is still lacking. In this paper, we report that while reviewing our old data recently, armed with a decade of knowledge, we realized that back in 2012 our results contained two breakthrough Majorana discoveries. Specifically, we have observed quantized zero-bias peaks, the hallmark of ideal Majorana states. Furthermore, we have observed the closing and re-opening of the induced gap perfectly correlated with the emergence of the zero-bias peak – clear evidence of the topological quantum phase superconducting transition. These insights should pave the way to topological Majorana qubits, and you should also check supplementary information for important disclosures.

A Few Almost Trivial Notes on the Symplectic Radon Transform and the Tomographic Picture of Quantum Mechanics. (arXiv:2203.17210v1 [quant-ph])

上午9:20

Maurice de Gosson

quant-ph updates on arXiv.org

We emphasize in these pedagogical notes the that the theory of the Radon transform and its applications is best understood using the theory of the metaplectic group and the quadratic Fourier transforms generating metaplectic operator.. Doing this we hope that these notes will be useful to a larger audience, including researchers in time-frequency analysis.

On free fall of quantum matter. (arXiv:2110.10056v2 [hep-th] UPDATED)

上午9:20

Viacheslav A. Emelyanov

quant-ph updates on arXiv.org

We propose an approach that allows to systematically take into account gravity in quantum particle physics. It is based on quantum field theory and the general principle of relativity. These are used to build a model for quantum particles in curved spacetime. We compute by its means a deviation from a classical geodesic in the Earth’s gravitational field. This shows that free fall depends on quantum-matter properties. Specifically, we find that the free-fall universality and the wave-packet spreading are mutually exclusive phenomena. We then estimate the E\”{o}tv\”{o}s parameter for a pair of atoms freely falling near the Earth’s surface, provided that the wave-packet spreading is more fundamental than the weak equivalence principle.

Wading through the void: Exploring quantum friction and nonequilibrium fluctuations. (arXiv:2112.12195v2 [quant-ph] UPDATED)

上午9:20

Daniel Reiche, Francesco Intravaia, Kurt Busch

quant-ph updates on arXiv.org

When two or more objects move relative to one another in vacuum, they experience a drag force which, at zero temperature, usually goes under the name of quantum friction. This contactless non-conservative interaction is mediated by the fluctuations of the material-modified quantum electrodynamic vacuum and, hence, is purely quantum in nature. Numerous investigations have revealed the richness of the mechanisms at work, thereby stimulating novel theoretical and experimental approaches and identifying challenges as well as opportunities. In this article, we provide an overview of the physics surrounding quantum friction and a perspective on recent developments.

Can quantum mechanics breed negative masses?. (arXiv:2112.08881v2 [gr-qc] CROSS LISTED)

上午9:20

Bruno Arderucio Costa, George E. A. Matsas

quant-ph updates on arXiv.org

The Casimir effect realizes the existence of static negative energy densities in quantum field theory. We establish physically reasonable conditions for the non-negativity of the total mass of a Casimir apparatus held in equilibrium in the Minkowski background, irrespectively of any condensed matter consideration. Specifically, the dynamical equilibrium requires the presence of additional matter to hold the system apart. As long as this extra matter satisfies the dominant energy condition, the mass of the combined system is positive. Thus, the very same reason why energy cannot travel backwards in time could be the underlying mechanism behind the positivity of the mass. We discuss the takeaways from the Casimir setting to more general circumstances.

Comment on Causal Networks and Freedom of Choice in Bell’s Theorem. (arXiv:2201.08483v2 [quant-ph] UPDATED)

上午9:20

Marian Kupczynski

quant-ph updates on arXiv.org

Bell inequalities may only be derived, if hidden variables do not depend on the experimental settings. The stochastic independence of hidden and setting variables is called: freedom of choice, free will, measurement independence or no conspiracy. By imbedding the Bell causal structure in a larger causal network the authors correctly prove, that one can explain and quantify possible violation of measurement independence without evoking the super-determinism. They assume the independence of the variables that causally determine the settings and investigate how they might become correlated with hidden variables. Using their extended causal networks they derive a contextual probabilistic model on which their further correct results are based. The authors seem to ignore that contextual probabilistic model may be derived directly using only probabilistic concepts and incorporating correctly setting dependent variables describing measuring instruments. In these contextual probabilistic models experimenters freedom of choice is not compromised and the results of Bell Tests including an apparent violation of Einsteinian nonsignaling may be explained in a locally causal way. Talking about freedom of choice is misleading and is rooted in incorrect understanding of Bayes Theorem. We explain why freedom of choice should be called noncontextuality and why its violation in Bell Tests confirms only the contextual character of quantum observables. Therefore, contextuality and not experimenters freedom of choice are important resources in quantum information.

Distillation of Indistinguishable Photons. (arXiv:2203.15197v2 [quant-ph] UPDATED)

上午9:20

Jeffrey Marshall

quant-ph updates on arXiv.org

A reliable source of identical (indistinguishable) photons is a prerequisite for exploiting interference effects, which is a necessary component for linear optical based quantum computing, and applications thereof such as Boson sampling. Generally speaking, the degree of distinguishability will determine the efficacy of the particular approach, for example by limiting the fidelity of constructed resource states, or reducing the complexity of an optical circuits output distribution. It is therefore of great practical relevance to engineer sources of highly indistinguishable photons. Inspired by magic state distillation, we present a protocol using standard linear optics (such as beamsplitters) which can be used to increase the indistinguishability of a photon source, to arbitrary accuracy. In particular, in the asymptotic limit of small error, we show that using 9 (16) photons one can distill a single purer photon, with error decreasing by 1/3 (1/4) per iteration. We demonstrate the scheme is robust to detection errors (such as dark counts) to second order.

Comparing constellations across cultures. (arXiv:2203.16649v1 [physics.hist-ph])

上午9:20

physics.hist-ph updates on arXiv.org

Authors: Charles Kemp, Duane W Hamacher, Daniel R Little, Simon J Cropper

Cultural astronomy reveals ways in which perception and culture have shaped the interpretation of the night sky.

Contemplating the fate of modified gravity. (arXiv:2203.16610v1 [gr-qc])

上午9:20

gr-qc updates on arXiv.org

Authors: Alexey Golovnev, Maria-Jose Guzman

Possible models of modified gravity are being extensively studied now, with most phenomenological motivations coming from puzzles and tensions in cosmology with a natural desire to better fit the known and newly coming data. At the same time, available experimental evidence is limited for testing gravity as a force, beyond the regimes in which the theory of general relativity has proven to be successful. This situation leads researchers to look for “the simplest modification” to general relativity, in a certain class of models, that is enough to solve one or more problems. As a result, we are lost amidst a variety of theories with no deeper guiding principle. In this essay, we openly discuss these problems, and propose some ideas on how to go.

Observable vacuum energy is finite in expanding space. (arXiv:2203.16753v1 [gr-qc])

上午9:20

gr-qc updates on arXiv.org

Authors: Csaba Balazs

In this work I reason that in expanding space only those quantum modes contribute to the measured vacuum energy that do not transcend the observable volume. Since all quantised field modes have various observable consequences, when a gravitational horizon causally confines an observer to a finite volume quantised modes should be restricted to the observable patch to remain consistent with gravity.

Within the observable patch of Friedmann-Lemaitre-Robertson-Walker (FLRW) space the vacuum expectation value of the energy-momentum tensor can be expressed as a sum over discrete field modes. Friedmann’s first equation provides a straightforward ultraviolet cut-off allowing only a finite number of modes in the sum. The finite volume acts as an infrared regulator and the calculation of the vacuum energy density is tractable without regularisation and renormalisation.

To test the validity of this idea I quantise a scalar field on an FLRW background and calculate its vacuum energy density in the vacuum dominated, conformal, holographic limit. In this limit I show that the quantum vacuum energy density scales with the square of the Hubble parameter, consistently with gravity. In this example quantum vacuum expands space while the horizon of the expanding space limits the energy density of the vacuum to the observed value.

Gravitizing the Quantum. (arXiv:2203.17137v1 [gr-qc])

上午9:20

gr-qc updates on arXiv.org

Authors: Per Berglund, Tristan Hübsch, David Mattingly, Djordje Minic

We discuss a new approach to the problem of quantum gravity in which the quantum mechanical structures that are traditionally fixed, such as the Fubini-Study metric in the Hilbert space of states, become dynamical and so implement the idea of gravitizing the quantum. In particular, in this formulation of quantum gravity the quantum geometry is still consistent with the principles of unitarity and also captures fundamental aspects of (quantum) gravity, such as topology change. Furthermore, we address specific ways of testing this new approach to quantum gravity by utilizing multi-path interference and optical lattice atomic clocks.

Microscopic black holes as probes for quantum gravity. (arXiv:2203.12332v2 [gr-qc] UPDATED)

上午9:20

gr-qc updates on arXiv.org

Authors: Samuel Kováčik

One of the main goals of contemporary theoretical physics is to find the quantum theory of gravity. There are various working hypotheses, mostly operating in the regime of high-energy physics well above the reach of particle accelerators. So far, strong experimental or observational evidence to guide the theory is missing. A possible consequence of quantum gravity and quantum spacetime that is often discussed is the vacuum dispersion effect. In this paper, we consider a different line of quantum space phenomenology, the behaviour of microscopic black holes. Even though their exact nature is unknown, some of their features are very model-independent, allowing us to draw conclusions about their role in the current cosmological models.

Singularity resolution in gravitational collapse. (arXiv:2110.07343v3 [gr-qc] UPDATED)

上午9:20

gr-qc updates on arXiv.org

Authors: Karim Mosani, Dipanjan Dey, Kaushik Bhattacharya, Pankaj S. Joshi

We investigate the unhindered gravitational collapse of a homogeneous scalar field with nonzero potential, a two-dimensional analog of the Mexican hat-shaped Higgs field potential. The collapsing scalar field is surrounded by an exterior retarded (outgoing) generalized Vaidya spacetime. We prove that the density dependence on the scale factor cannot be expressed as an algebraic function in such a scenario. For a certain transcendental expression of the density of such field as a function of scale factor, we then show that the collapse evolves to a singularity at an infinite comoving time, which is equivalent to saying that the singularity is avoided altogether. An ultra high density region of the order of Planck length can, however, be reached in a finite comoving time. The absence of the formation of trapped surfaces makes this ultra high density region globally visible.

One world is (probably) just as good as many

2022年4月1日星期五下午4:15