A healthier semi-classical dynamics. (arXiv:2208.11722v1 [quant-ph])

上午10:02 | | | Isaac Layton, Jonathan Oppenheim, Zachary Weller-Davies | | | quant-ph updates on arXiv.org |

We study the back-reaction of quantum systems onto classical ones. Taking the starting point that semi-classical physics should be described at all times by a point in classical phase space and a quantum state in Hilbert space, we consider an unravelling approach, describing the system in terms of a classical-quantum trajectory. We derive the general form of the dynamics under the assumptions that the classical trajectories are continuous and the evolution is autonomous, and the requirement that the dynamics is linear and completely positive in the combined classical-quantum state. This requirement is necessary in order to consistently describe probabilities, and forces the dynamics to be stochastic when the back-reaction is non-zero. The resulting equations of motion are natural generalisations of the standard semi-classical equations of motion, but since the resulting dynamics is linear in the combined classical-quantum state, it does not lead to the pathologies which usually follow from evolution laws based on expectation values. In particular, the evolution laws we present account for correlations between the classical and quantum system, which resolves issues associated with other semi-classical approaches. In addition, despite a breakdown of predictability in the classical degrees of freedom, the quantum state evolves deterministically conditioned on the classical trajectory, provided a trade-off between decoherence and diffusion is saturated. As a result, the quantum state remains pure when conditioned on the classical trajectory. To illustrate these points, we numerically simulate a number of semi-classical toy models, including one of vacuum fluctuations as a source driving the expansion of the universe. Finally, we discuss the application of these results to semi-classical gravity, and the black-hole information problem.

Quantum superpositions of Minkowski spacetime. (arXiv:2208.12083v1 [gr-qc])

上午10:02 | | | Joshua Foo, Cemile Senem Arabaci, Magdalena Zych, Robert B. Mann | | | quant-ph updates on arXiv.org |

Within any anticipated unifying theory of quantum gravity, it should be meaningful to combine the fundamental notions of quantum superposition and spacetime to obtain so-called “spacetime superpositions”: that is, quantum superpositions of different spacetimes not related by a global coordinate transformation. Here we consider the quantum-gravitational effects produced by superpositions of periodically identified Minkowski spacetime (i.e.\ Minkowski spacetime with a periodic boundary condition) with different characteristic lengths. By coupling relativistic quantum matter to fields on such a spacetime background (which we model using the Unruh-deWitt particle detector model), we are able to show how one can in-principle “measure” the field-theoretic effects produced by such a spacetime. We show that the detector’s response exhibits discontinuous resonances at rational ratios of the superposed periodic length scale.

上午10:02 | | | Sabre Kais | | | quant-ph updates on arXiv.org |

Classical phase transitions, like solid-liquid-gas or order-disorder spin magnetic phases, are all driven by thermal energy fluctuations by varying the temperature. On the other hand, quantum phase transitions happen at absolute zero temperature with quantum fluctuations causing the ground state energy to show abrupt changes as one varies the system parameters like electron density, pressure, disorder, or external magnetic field. Phase transitions happen at critical values of the controlling parameters, such as the critical temperature in classical phase transitions, and system critical parameters in the quantum case. However, true criticality happens only at the thermodynamic limit, when the number of particles goes to infinity with constant density. To perform the calculations for the critical parameters, finite size scaling approach was developed to extrapolate information from a finite system to the thermodynamic limit. With the advancement in the experimental and theoretical work in the field of ultra-cold systems, particularly trapping and controlling single atomic and molecular systems, one can ask: do finite systems exhibit quantum phase transition? To address this question, finite size scaling for finite system was developed to calculate the quantum critical parameters. Recent observation of a quantum phase transition in a single trapped 171 Yb ion in the Paul trap indicates the possibility of quantum phase transition in finite systems. This perspective focuses on examining chemical processes at ultracold temperature as quantum phase transitions, particularly the formation and dissociation of chemical bonds, which is the basic process for understanding the whole of chemistry

Testing Quantum Mechanics using Noisy Quantum Computers. (arXiv:2108.02201v4 [quant-ph] UPDATED)

上午10:02 | | | Kevin Slagle | | | quant-ph updates on arXiv.org |

We outline a proposal to test quantum mechanics in the high-complexity regime using noisy intermediate-scale quantum (NISQ) devices. The procedure involves simulating a non-Clifford random circuit, followed by its inverse, and then checking that the resulting state is the same as the initial state. We are motivated by the hypothesis that quantum mechanics is not fundamental, but instead emerges from a theory with less computational power, such as classical mechanics. This emergent quantum mechanics (EmQM) hypothesis makes the prediction that quantum computers will not be capable of sufficiently complex quantum computations. We show that quantum mechanics predicts that the fidelity of our procedure decays exponentially with circuit depth (due to noise in NISQ devices), while EmQM predicts that the fidelity will decay significantly more rapidly for sufficiently deep circuits, which is the experimental signature that we propose to search for. We estimate rough bounds for when possible signals of EmQM should be expected. Furthermore, we find that highly informative experiments should require only thousands qubits.

上午10:02 | | | physics.hist-ph updates on arXiv.org |

Authors: Martin Korth

The tremendous advances of research into artificial intelligence as well as neuroscience made over the last two to three decades have given further support to a renewed interest into philosophical discussions of the mind-body problem. Especially the last decade has seen a revival of panpsychist and idealist considerations, often focused on solving philosophical puzzles like the so-called hard problem of consciousness. While a number of respectable philosophers advocate some sort of panpsychistic solution to the mind-body problem now, fewer advocate that idealism can contribute substantially to the debate. Interest in idealism has nevertheless risen again, as can be seen also from recent overview articles and collections of works. The working hypothesis here is that a properly formulated idealism can not only provide an alternative view of the mind/matter gap, but that this new view will also shed light on open questions in our common scientific, i.e. materialist, world view. To investigate this possibility, idealism first of all needs a model for the integration of modern science which allows for a mathematically consistent reinterpretation of the physical world as a limiting case of a both material and non-material world, which would make the outcome of idealistic considerations accessible to scientific investigation. To develop such a model I will first try to explain what I mean when I speak of a ‘scientifically tenable’ idealism, including a formulation of the emanation problem which for idealism replaces the interaction problem, then give a very brief summary of the available elements of such a theory in the philosophical literature, before sketching out some ‘design questions’ which have to be answered upon the construction of such models, and finally put forward a first model for a scientifically tenable objective idealism.

Quantum Gravitational Decoherence in the 3 Neutrino Flavor Scheme. (arXiv:2208.11754v1 [hep-ph])

上午10:02 | | | gr-qc updates on arXiv.org |

Authors: Dominik Hellmann, Heinrich Päs, Erika Rani

In many theories of quantum gravity quantum fluctuations of spacetime may serve as an environment for decoherence. Here we study quantum-gravitational decoherence of high energy astrophysical neutrinos in the presence of fermionic dark sectors and for a realistic three neutrino scenario. We show how violation of global symmetries expected to arise in quantum gravitational interactions provides a possibility to pin down the number of dark matter fermions in the universe. Furthermore, we predict the expected total neutrino flux and flavor ratios at experiments depending on the flavor composition at the source.

Neutrino Decoherence from Generalised Uncertainty. (arXiv:2208.12062v1 [hep-ph])

上午10:02 | | | gr-qc updates on arXiv.org |

Authors: Indra Kumar Banerjee, Ujjal Kumar Dey

Quantum gravity models predict a minimal measurable length which gives rise to a modification in the uncertainty principle. One of the simplest manifestations of these generalised uncertainty principles is the linear quadratic generalised uncertainty principle which leads to a modified Heisenberg algebra. This can alter the usual von-Neumann evolution of density matrix to a Lindblad-type equation. We show how this can give rise to decoherence in neutrino propagation in vacuum. The decoherence effects due to the linear quadratic generalised uncertainty principle are extremely minimal and are unlikely to be detectable in the existing or upcoming experimental facilities for any of the natural sources of neutrinos. We also show that, in principle, there can be other variants of generalised uncertainty principle which predict verifiable decoherence effects for the cosmic neutrino background.

How (and Why) to Think that the Brain is Literally a Computer

2022年8月25日 星期四 下午1:57 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

Maley, Corey J. (2022) How (and Why) to Think that the Brain is Literally a Computer. [Preprint]

Experiments with levitated force sensor challenge theories of dark energy

2022年8月25日 星期四 上午8:00 | | | Jiangfeng Du | | | Nature Physics – Issue – nature.com science feeds |

Nature Physics, Published online: 25 August 2022; doi:10.1038/s41567-022-01706-9

In experiments with a levitated force sensor, no signatures of a fifth force are detected. This rules out the basic chameleon model, which is a popular theory providing an explanation for dark energy.

Ehrenfest Theorems, Deformation Quantization, and the Geometry of Inter-Model Reduction

2022年8月25日 星期四 上午12:55 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

Rosaler, Joshua (2018) Ehrenfest Theorems, Deformation Quantization, and the Geometry of Inter-Model Reduction. Generalized Ehrenfest Relations, Deformation Quantization, and the Geometry of Inter-Model Reduction.

Do quantum observers have minds?

2022年8月25日 星期四 上午12:50 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

Gao, Shan (2022) Do quantum observers have minds? [Preprint]

Superdeterminism: a reappraisal

2022年8月24日 星期三 上午8:00 | | | Latest Results for Synthese |

**Abstract**

This paper addresses a particular interpretation of quantum mechanics, i.e. superdeterminism. In short, superdeterminism i) takes the world to be fundamentally deterministic, ii) postulates hidden variables, and iii) contra Bell, saves locality at the cost of violating the principle of statistical independence. Superdeterminism currently enjoys little support in the physics and philosophy communities. Many take it to posit the ubiquitous occurrence of hard-to-digest conspiratorial and coincidental events; others object that violating the principle of statistical independence implies the death of the scientific methodology. In this paper, we offer a defense to these and other objections. To counter the conspiracy objection, we draw upon the philosophical literature on time travel, and conclude that the picture of the world offered by the superdeterminist does not need to be particularly surprising or conspiratorial. We then move on to other recent objections, in particular those that focus on the methodology of science and the nature of the physical laws compatible with superdeterminism. A key ingredient of our arguments is that the principle of statistical independence may be violated *in theory*, but valid *for practical purposes*. Our overarching goal is to offer a defense of superdeterminism with respect to its main objections, so that it can earn its keep as a legitimate contender among the possible interpretations of quantum mechanics.

Empty space and the (positive) cosmological constant

2022年8月20日 星期六 下午11:06 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. |

Schneider, Mike D. (2022) Empty space and the (positive) cosmological constant. [Preprint]