2019年12月6日 星期五 下午7:47 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

2019年12月6日 星期五 下午6:00 | | | Giacomo Torlai, Brian Timar, Evert P. L. van Nieuwenburg, Harry Levine, Ahmed Omran, Alexander Keesling, Hannes Bernien, Markus Greiner, Vladan Vuletić, Mikhail D. Lukin, Roger G. Melko, and Manuel Endres | | | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc. |

Author(s): Giacomo Torlai, Brian Timar, Evert P. L. van Nieuwenburg, Harry Levine, Ahmed Omran, Alexander Keesling, Hannes Bernien, Markus Greiner, Vladan Vuletić, Mikhail D. Lukin, Roger G. Melko, and Manuel Endres

An array of nine strongly interacting Rydberg atoms is used for a proof-of-principle demonstration of neural-network quantum state reconstruction.

[Phys. Rev. Lett. 123, 230504] Published Fri Dec 06, 2019

2019年12月5日 星期四 上午6:08 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

2019年12月4日 星期三 下午5:25 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

2019年12月4日 星期三 上午9:04 | | | Philipp A. Hoehn, Alexander R. H. Smith, Maximilian P. E. Lock | | | quant-ph updates on arXiv.org |

The problem of time in quantum gravity calls for a relational solution. Using quantum reduction maps, we establish a previously unknown equivalence between three approaches to relational quantum dynamics: 1) relational observables in the clock-neutral picture of Dirac quantization, 2) Page and Wootters’ (PW) Schr\”odinger picture formalism, and 3) the relational Heisenberg picture obtained via symmetry reduction. Constituting three faces of the same dynamics, we call this equivalence the trinity. We develop a quantization procedure for relational Dirac observables using covariant POVMs which encompass non-ideal clocks. The quantum reduction maps reveal this procedure as the quantum analog of gauge-invariantly extending gauge-fixed quantities. We establish algebraic properties of these relational observables. We extend a recent `clock-neutral’ approach to changing temporal reference frames, transforming relational observables and states, and demonstrate a clock dependent temporal nonlocality effect. We show that Kucha\v{r}’s criticism, alleging that the conditional probabilities of the PW formalism violate the constraint, is incorrect. They are a quantum analog of a gauge-fixed description of a gauge-invariant quantity and equivalent to the manifestly gauge-invariant evaluation of relational observables in the physical inner product. The trinity furthermore resolves a previously reported normalization ambiguity and clarifies the role of entanglement in the PW formalism. The trinity finally permits us to resolve Kucha\v{r}’s criticism that the PW formalism yields wrong propagators by showing how conditional probabilities of relational observables give the correct transition probabilities. Unlike previous proposals, our resolution does not invoke approximations, ideal clocks or ancilla systems, is manifestly gauge-invariant, and easily extends to an arbitrary number of conditionings.

2019年12月4日 星期三 上午9:04 | | | Adam R. Brown, Hrant Gharibyan, Geoff Penington, Leonard Susskind | | | quant-ph updates on arXiv.org |

According to Harlow and Hayden [arXiv:1301.4504] the task of distilling information out of Hawking radiation appears to be computationally hard despite the fact that the quantum state of the black hole and its radiation is relatively un-complex. We trace this computational difficulty to a geometric obstruction in the Einstein-Rosen bridge connecting the black hole and its radiation. Inspired by tensor network models, we conjecture a precise formula relating the computational hardness of distilling information to geometric properties of the wormhole – specifically to the exponential of the difference in generalized entropies between the two non-minimal quantum extremal surfaces that constitute the obstruction. Due to its shape, we call this obstruction the “Python’s Lunch”, in analogy to the reptile’s postprandial bulge.

2019年12月4日 星期三 上午9:04 | | | Massimo Blasone, Gaetano Lambiase, Giuseppe Gaetano Luciano, Luciano Petruzziello, Fabio Scardigli | | | quant-ph updates on arXiv.org |

We propose a heuristic derivation of Casimir effect in the context of minimal length theories based on a Generalized Uncertainty Principle (GUP). By considering a GUP with only a quadratic term in the momentum, we compute corrections to the standard formula of Casimir energy for the parallel-plate geometry, the sphere and the cylindrical shell. For the first configuration, we show that our result is consistent with the one obtained via more rigorous calculations in Quantum Field Theory. Experimental developments are finally discussed.

2019年12月4日 星期三 上午9:04 | | | Juerg Froehlich | | | quant-ph updates on arXiv.org |

The purpose of this paper is to sketch an approach towards a reconciliation of quantum theory with relativity theory. It will actually be argued that these two theories ultimately rely on one another. A general operator-algebraic framework for relativistic quantum theory is outlined. Some concepts of space-time structure are translated into algebra. Following deep results of Buchholz et al., the key role of massless modes, photons and gravitons, and of Huygens’ Principle in a relativistic quantum theory well suited to describe “events” and “measurements” is highlighted. In summary, a relativistic version of the “ETH Approach” to quantum mechanics is described.

2019年12月4日 星期三 上午9:04 | | | Ying Zhao | | | quant-ph updates on arXiv.org |

We give a complexity interpretation of evaporating black hole geometry. We make an analogy between the appearance of island for evaporating black hole and the transition from two-sided to one-sided black hole in the familiar example of perturbed thermofield double. If Alice perturbs thermofield double and waits for scrambling time, she will have a one-sided black hole with interior of her own. We argue that by similar mechanism the radiation gets access to the interior (island forms) after Page time. The growth of the island happens as a result of the constant transitions from two-sided to one-sided black holes.

2019年12月4日 星期三 上午9:04 | | | Richard D. Gill | | | quant-ph updates on arXiv.org |

Pearle (1970) gave an example of a local hidden variables model which exactly reproduced the singlet correlations of quantum theory, through the device of data-rejection: particles can fail to be detected in a way which depends on the hidden variables carried by the particles and on the measurement settings. If the experimenter computes correlations between measurement outcomes of particle pairs for which both particles are detected, he is actually looking at a subsample of particle pairs, determined by interaction involving both measurement settings and the hidden variables carried in the particles. We correct a mistake in Pearle’s formulas (a normalization error) and more importantly show that the model is more simple than first appears. We illustrate with visualisations of the model and with a small simulation experiment, with code in the statistical programming language R included in the paper. Open problems are discussed.

2019年12月4日 星期三 上午9:04 | | | Manuel Gessner, Heinz-Peter Breuer | | | quant-ph updates on arXiv.org |

How can we detect that our local, controllable quantum system is correlated with some other inaccessible environmental system? The local detection method developed in recent years allows to realize a dynamical witness for correlations without requiring knowledge of or access to the environment that is correlated with the local accessible quantum system. Here, we provide a brief summary of the theoretical method and recent experimental studies with single photons and trapped ions coupled to increasingly complex environments.

2019年12月4日 星期三 上午9:04 | | | J. Jeknic-Dugic, M. Arsenijevic, M. Dugic | | | quant-ph updates on arXiv.org |

Assuming the unitary-only dynamics for the “open system plus environment” composite quantum system, for certain typical Markovian models we find that the standard ignorance-based ensemble interpretation of the open system’s dynamics fails. Our analysis is purely technical and within the standard quantum-mechanical formalism without employing or calling for any additional assumptions. Conceptual implications are presented in comparison with some related results, which include the so-called master equation unraveling in quantum optics, the so-called continuous spontaneous localization theory as well as the concept of mixed states applied to single quantum systems.

2019年12月4日 星期三 上午9:04 | | | Klaas Landsman | | | quant-ph updates on arXiv.org |

This is a review of the issue of randomness in quantum mechanics, with special emphasis on its ambiguity; for example, randomness has different antipodal relationships to determinism, computability, and compressibility. Following a (Wittgensteinian) philosophical discussion of randomness in general, I argue that deterministic interpretations of quantum mechanics (like Bohmian mechanics or ‘t Hooft’s Cellular Automaton interpretation) are strictly speaking incompatible with the Born rule. I also stress the role of outliers, i.e. measurement outcomes that are not 1-random. Although these occur with low (or even zero) probability, their very existence implies that the no-signaling principle used in proofs of randomness of outcomes of quantum-mechanical measurements (and of the safety of quantum cryptography) should be reinterpreted statistically, like the second law of thermodynamics. In appendices I discuss the Born rule and its status in both single and repeated experiments, and review the notion of 1-randomness introduced by Kolmogorov, Chaitin, Martin-Lo”f, Schnorr, and others.

2019年12月4日 星期三 上午9:04 | | | Fabio Benatti, Stefano Mancini, Stefano Mangini | | | quant-ph updates on arXiv.org |

We present a model of Continuous Variable Quantum Perceptron (CVQP) whose architecture implements a classical perceptron. The necessary non-linearity is obtained via measuring the output qubit and using the measurement outcome as input to an activation function. The latter is chosen to be the so-called ReLu activation function by virtue of its practical feasibility and the advantages it provides in learning tasks. The encoding of classical data into realistic finitely squeezed states and the use of superposed (entangled) input states for specific binary problems are discussed.

2019年12月4日 星期三 上午9:04 | | | physics.hist-ph updates on arXiv.org |

Authors: Zhixin Wang

This short essay traces the conceptual history of micro- and macroscopicity in the context of physical science. By focusing on three distinct episodes spanning five centuries, we show the scientific and philosophical meanings of this antonym pair, despite never being far from “the small” and “the large,” have been evolving as the frontier of science advances. We analyze the intellectual and material impetus for these movements, and conclude that this conceptual history reflects the changing interaction between the natural world and humankind.

2019年12月4日 星期三 上午9:04 | | | gr-qc updates on arXiv.org |

Authors: Miaoxin Liu, Zhiqi Huang, Xiaolin Luo, Haitao Miao, Naveen K. Singh, Lu Huang

The inconsistent Hubble constant values derived from cosmic microwave background (CMB) observations and from local distance-ladder measurements may suggest new physics beyond the standard $\Lambda$CDM paradigm. It has been found in earlier works that, at least phenomenologically, non-standard recombination histories can reduce the $\gtrsim 4\sigma$ Hubble tension to $\sim 2\sigma$. Following this path, we vary physical and phenomenological parameters in RECFAST, the standard code to compute ionization history of the universe, to explore possible physics beyond standard recombination. We find that the CMB constraint on the Hubble constant is sensitive to the Hydrogen ionization energy and $2s \rightarrow 1s$ two-photon decay rate, both of which are atomic constants, and is insensitive to other details of recombination. Thus, the Hubble tension is very robust against perturbations of recombination history, unless exotic physics modifies the atomic constants during the recombination epoch.

2019年12月4日 星期三 上午9:04 | | | gr-qc updates on arXiv.org |

Authors: Péter Ván, Sumiyoshi Abe

Being inspired by Verlinde’s proposal that general relativistic gravity has a thermodynamic origin as an entropic force, Newtonian gravity is reexamined in view of nonequilibrium thermodynamics. Here, firstly, an unspecified scalar field potential is introduced and treated as a thermodynamic variable on an equal footing with the fluid variables. Then, the effects of irreversibility on the field are explored through the analysis of the entropy production rate in the linear regime. Remarkably, the second law of thermodynamics imposes a stringent constraint on the allowable field, which turns out to be of gravity. The resulting field equation for the gravitational potential contains a dissipative term originating from irreversibility. It is found that the system relaxes to the conventional theory of Newtonian gravity up to a certain spatial scale (typically the solar scale), whereas on the larger scale (such as the galaxy scale) a potential needed in Modified Newtonian Dynamics (MOND) naturally appears. A comment is made on an implication of the result to the astrophysical phenomenon regarding dark matter.

2019年12月4日 星期三 上午9:04 | | | gr-qc updates on arXiv.org |

Authors: Rong-Gen Cai, Shao-Jiang Wang

We propose a refined version of trans-Planckian censorship conjecture (TCC), which could be elaborated from the strong scalar weak gravity conjecture combined with some entropy bounds. In particular, no fine-tuning on the inflation model-building is required in the refined TCC, and it automatically passes the tests from those stringy examples that support the original TCC.

2019年12月4日 星期三 上午9:04 | | | gr-qc updates on arXiv.org |

Authors: Robert H. Sanders

The dark energy-cold dark matter paradigm ($\Lambda$CDM) has gained widespread acceptance because it explains the pattern of anisotropies observed in the cosmic microwave background radiation, the observed distribution of large scale inhomogeneities in detectable matter, and the perceived overall expansion history of the Universe. It is further {\it assumed} that the cosmic dark matter component clusters on the scale of bound astronomical systems and thereby accounts for the observed difference between the directly detectable (baryonic) mass and the total Newtonian dynamical mass. In this respect the paradigm fails; it is falsified by the existence of a simple algorithm, modified Newtonian dynamics (MOND), which explains, not only general scaling relations for astronomical systems, but quite precisely predicts the effective gravitational acceleration in such objects from the observed distribution of detectable baryonic matter — all of this with one additional universal parameter having units of acceleration. On this sub-Hubble scale, the dark matter hypothesis is essentially reactive, while MOND is successfully predictive.

2019年12月4日 星期三 上午9:04 | | | gr-qc updates on arXiv.org |

Authors: C. Wetterich

We propose the great emptiness as a possible beginning of the Universe in the infinite past of physical time. In the beginning particles are very rare and effectively massless. Only expectation values of fields and average fluctuations characterize the lightlike vacuum of this empty Universe. Our observed inhomogeneous Universe can be extrapolated backwards to the lightlike vacuum in the infinite past, and therefore can have lasted eternally. There is no physical big bang singularity. Standard inflation models admit a primordial flat frame for which spacetime is flat in the infinite past.

2019年12月4日 星期三 上午9:04 | | | gr-qc updates on arXiv.org |

Authors: George F R Ellis, Barbara Drossel

Microphysical laws are time reversible, but macrophysics, chemistry and biology are not. This chapter explores how this asymmetry (a classic example of a broken symmetry) arises due to the cosmological context, where a non-local Direction of Time is imposed by the expansion of the universe. This situation is best represented by an Evolving Block Universe, where local arrows of time (thermodynamic, electrodynamic, gravitational, wave, quantum, biological) emerge in concordance with the Direction of Time because a global Past Condition results in the Second Law of Thermodynamics pointing to the future. At the quantum level, the indefinite future changes to the definite past due to quantum wave function collapse events.

2019年12月3日 星期二 下午6:00 | | | Lei Xiao, Kunkun Wang, Xiang Zhan, Zhihao Bian, Kohei Kawabata, Masahito Ueda, Wei Yi, and Peng Xue | | | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc. |

Author(s): Lei Xiao, Kunkun Wang, Xiang Zhan, Zhihao Bian, Kohei Kawabata, Masahito Ueda, Wei Yi, and Peng Xue

We experimentally simulate nonunitary quantum dynamics using a single-photon interferometric network and study the information flow between a parity-time- (PT-)symmetric non-Hermitian system and its environment. We observe oscillations of quantum-state distinguishability and complete information ret…

[Phys. Rev. Lett. 123, 230401] Published Tue Dec 03, 2019

2019年12月3日 星期二 下午4:41 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

2019年12月3日 星期二 上午8:00 | | | Meehan A. | | | The British Journal for the Philosophy of Science Advance Access |

In this article I raise a new problem for quantum mechanics, which I call the control problem. Like the measurement problem, the control problem places a fundamental constraint on quantum theories. The characteristic feature of the problem is its focus on state preparation. In particular, whereas the measurement problem turns on a premise about the completeness of the quantum state (‘no hidden variables’), the control problem turns on a premise about our ability to prepare or control quantum states. After raising the problem, I discuss some applications. I suggest that it provides a useful new lens through which to view existing theories or interpretations, in part because it draws attention to aspects of those theories that the measurement problem does not (such as the role of conditional and relative states). I suggest that it also helps clarify the physical significance of the well-known no-go result—the no-cloning theorem—on which it is based.

2019年12月2日 星期一 下午1:41 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

2019年12月2日 星期一 上午8:00 | | | Stefanie Reichert | | | Nature Physics – Issue – nature.com science feeds |

Nature Physics, Published online: 02 December 2019; doi:10.1038/s41567-019-0755-6

The Universe before our time

2019年12月2日 星期一 上午8:00 | | | Nature Physics – Issue – nature.com science feeds |

Nature Physics, Published online: 02 December 2019; doi:10.1038/s41567-019-0758-3

Taking the expectation value of an observable is not the same as averaging over time.

2019年12月2日 星期一 上午8:00 | | | Latest Results for Foundations of Physics |

### Abstract

A large number of physicists now admit that quantum mechanics is a non-local theory. The EPR argument and the many experiments (including recent “loop-hole free” tests) showing the violation of Bell’s inequalities seem to have confirmed convincingly that quantum mechanics cannot be local. Nevertheless, this conclusion can only be drawn inside a standard realist framework assuming an ontic interpretation of the wave function and viewing the collapse of the wave function as a real change of the physical state of the system. We show that this standpoint is not mandatory and that if the collapse is not considered an actual physical change it is possible to recover locality.