Weekly Papers on Quantum Foundations (46)

上午8:00 | Latest Results for Synthese

Abstract

I conceptualise the role of dualities in quantum gravity, in terms of their functions for theory construction. I distinguish between two functions of duality in physical practice: namely, discovering and describing ‘equivalent physics’, versus suggesting ‘new physics’. I dub these the ‘theoretical’ versus the ‘heuristic’ functions of dualities. The distinction seems to have gone largely unnoticed in the philosophical literature: and it exists both for dualities, and for the more general relation of theoretical equivalence. The paper develops the heuristic function of dualities: illustrating how they can be used, if one has any luck, to find and formulate new theories. I also point to the different physical commitments about the theories in question that underlie these two functions. I show how a recently developed schema for dualities articulates the differences between the two functions.

上午8:00 | Latest Results for Foundations of Physics

Abstract

The debate on the conventionality of simultaneity and the debate on the dimensionality of the world have been central in the philosophy of special relativity. The link between both debates however has rarely been explored. The purpose of this paper is to gauge what implications the former debate has for the latter. I show the situation to be much more subtle than was previously argued, and explain how the ontic versus epistemic distinction in the former debate impacts the latter. Despite claims to the contrary, I conclude that special relativity leaves the debate on the dimensionality of the world underdetermined.

上午8:00 | Latest Results for Foundations of Physics

Abstract

What is simultaneous with an event is what can interact with it; events have duration; therefore, any given event has distant events simultaneous with it, even according to Special Relativity. Consequently, the extension of our pre-relativistic judgments of distant simultaneity are largely preserved.

上午8:00 | Latest Results for Foundations of Physics

Abstract

We point out a fundamental problem that hinders the quantization of general relativity: quantum mechanics is formulated in terms of systems, typically limited in space but infinitely extended in time, while general relativity is formulated in terms of events, limited both in space and in time. Many of the problems faced while connecting the two theories stem from the difficulty in shoe-horning one formulation into the other. A solution is not presented, but a list of desiderata for a quantum theory based on events is laid out.

上午8:00 | Latest Results for Foundations of Physics

Abstract

The classical limit is fundamental in quantum mechanics. It means that quantum predictions must converge to classical ones as the macroscopic scale is approached. Yet, how and why quantum phenomena vanish at the macroscopic scale is difficult to explain. In this paper, quantum predictions for Greenberger–Horne–Zeilinger states with an arbitrary number q of qubits are shown to become indistinguishable from the ones of a classical model as q increases, even in the absence of loopholes. Provided that two reasonable assumptions are accepted, this result leads to a simple way to explain the classical limit and the vanishing of observable quantum phenomena at the macroscopic scale.

上午8:00 | Latest Results for Foundations of Physics

Abstract

A recent paper (Martin-Dussaud et al. in Found Phys 49:96, 2019) has given a lucid treatment of Bell’s notion of local causality within the framework of the relational interpretation of quantum mechanics. However, the authors went on to conclude that the quantum violation of Bell’s notion of local causality is no more surprising than a common cause. Here, I argue that this conclusion is unwarranted by the authors’ own analysis. On the contrary, within the framework outlined by the authors, I argue that far from saving the notion of ‘locality’ from the grip of Bell’s theorem, the authors have deprived it of a meaningful definition.

上午8:00 | Latest Results for Foundations of Physics

Abstract

Is reality three-dimensional and becoming real (Presentism), or is reality four-dimensional and becoming illusory (Eternalism)? Both options raise difficulties. I argue that we do not need to be trapped by this dilemma. There is a third possibility: reality has a more complex temporal structure than either of these two naive options. Fundamental becoming is real, but local and unoriented. A notion of present is well defined, but only locally and in the context of approximations.

上午8:00 | Latest Results for Foundations of Physics

Abstract

Although Bohr’s Correspondence Principle (CP) played a central role in the first days of quantum mechanics, its original version seems to have no present-day relevance. The purpose of this article is to show that the CP, with no need of being interpreted in terms of the quantum-to-classical limit, still plays a relevant role in the understanding of the relationships between the classical and the quantum domains. In particular, it will be argued that a generic version of the CP is very helpful in elucidating the physical meaning of the phenomenon of quantum decoherence.

2019年11月22日 星期五 下午4:38 | quant-ph updates on arXiv.org

Authors: Adam Bene WattsNicole Yunger HalpernAram Harrow

The correspondence principle suggests that quantum systems grow classical when large. Classical systems cannot violate Bell inequalities, as entanglement can. Still, limited Bell-type inequalities have been proved for certain large-scale systems. We generalize and simplify these results, proving a nonlinear Bell inequality for macroscopic measurements. Our construction requires only bipartite measurements of extensive observables that have clear physical significances, governs fermions and bosons, and is robust with respect to errors whose variances scale as the system size. The result relies on limitations on particles’ interactions. A product of singlets violates the inequality. Experimental tests are feasible for photons, solid-state systems, atoms, and trapped ions. We operationalize the inequality as a nonlocal game whose players’ probability of winning is not averaged over questions. Consistently with known results, violations of our Bell inequality cannot disprove local hidden-variables theories. By rejecting the disproof goal, we show, one can certify nonclassical correlations under reasonable experimental assumptions.

2019年11月22日 星期五 下午4:38 | quant-ph updates on arXiv.org

Authors: Fabio BenattiStefano ManciniStefano Mangini

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11月22日 星期五 下午4:38 | quant-ph updates on arXiv.org

Authors: Maximilian Schlosshauer

I give a pedagogical overview of decoherence and its role in providing a dynamical account of the quantum-to-classical transition. The formalism and concepts of decoherence theory are reviewed, followed by a survey of master equations and decoherence models. I also discuss methods for mitigating decoherence in quantum information processing and describe selected experimental investigations of decoherence processes.

2019年11月22日 星期五 下午4:38 | quant-ph updates on arXiv.org

Authors: Ricardo Heras

The existence of the Aharonov-Bohm phase shows that the magnetic field may produce nonlocal effects in quantum mechanics. It is generally believed that such a nonlocal behavior of the magnetic field is not possible in classical physics and that this represents a clear difference between classical and quantum mechanics. Contrary to these beliefs, we argue that the classical counterpart of the Aharonov-Bohm phase, which is identified here with the electromagnetic angular momentum of the configuration formed by an electric charge moving around an infinitely-long solenoid enclosing a uniform magnetic flux, shows that the magnetic field may produce nonlocal effects in classical mechanics. We discuss this momentum in detail by putting special emphasis on its topological and nonlocal features. The momentum is topological because it depends on the number of windings the electric charge carries out around the solenoid and is nonlocal because the magnetic flux has no local consequences at any point on the charge trajectory. The topological feature allows us to introduce the concept of accumulated electromagnetic angular momentum and the nonlocal feature allows us to speak of a dynamical nonlocality attributable to the equations of classical electrodynamics.

2019年11月22日 星期五 下午4:38 | gr-qc updates on arXiv.org

Authors: C. N. KozamehJ. I. NievaG. D. Quiroga

The center of mass and spin for isolated sources of gravitational radiation that move at relativistic speeds are defined. As a first step, we also present these definitions in flat space. This contradicts some general wisdom given in textbooks claiming that such definitions are not covariant and thus, have no physical meaning. We then generalize the definitions to asymptotically flat spacetimes giving their equations of motion when gravitational radiation is emitted by the isolated sources. The resulting construction has some similarities with the Mathisson-Papapetrou equations which describes the motion of the particle in an external field. We analyze the relationship between the center of mass velocity and the Bondi linear momentum and show they are not proportional to each other. A similar situation happens between the total and intrinsic angular momentum when the Bondi momentum vanishes. We claim that extra terms should be added in other approaches to adequately describe the time evolution of isolated sources of gravitational radiation.

Authors: Niayesh Afshordi (U-Waterloo and Perimeter)

One of the most ubiquitous features of quantum theories is the existence of zero-point fluctuations in their ground states. For massive quantum fields, these fluctuations decouple from infrared observables in ordinary field theories. However, there is no “decoupling theorem” in Quantum Gravity, and we recently showed that the vacuum stress fluctuations of massive quantum fields source a red spectrum of metric fluctuations given by $\sim$ mass$^5$/frequency in Planck units. I show that this signal is consistent with the reported unattributed persistent noise, or “mystery” noise, in the Laser Interferometer Gravitational-Wave Observatory (LIGO), for the Standard Model of Particle Physics. If this interpretation is correct, then it implies that: 1) This will be a fundamental irreducible noise for all gravitational wave interferometers, and 2) There is no fundamental weakly-coupled massive particle heavier than those in the Standard Model.

2019年11月22日 星期五 下午4:38 | gr-qc updates on arXiv.org

Authors: John F. Donoghue

The present practice of Asymptotic Safety in gravity is in conflict with explicit calculations in low energy quantum gravity. This raises the question of whether the present practice meets the Weinberg condition for Asymptotic Safety. I argue, with examples, that the running of $\Lambda$ and $G$ found in Asymptotic Safety are not realized in the real world, with reasons which are relatively simple to understand. A comparison/contrast with quadratic gravity is also given, which suggests a few obstacles that must be overcome before the Lorentzian version of the theory is well behaved. I make a suggestion on how a Lorentzian version of Asymptotic Safety could potentially solve these problems.

2019年11月22日 星期五 上午8:04 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Kryukov, Alexey (2019) The classical and the quantum. [Preprint]
2019年11月21日 星期四 下午6:20 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Feintzeig, Benjamin (2019) Reductive Explanation and the Construction of Quantum Theories. [Preprint]
2019年11月21日 星期四 下午6:16 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Salimkhani, Kian (2018) Quantum Gravity: A Dogma of Unification? Philosophy of Science, 9. pp. 23-41. ISSN 2365-4228
2019年11月21日 星期四 下午6:15 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Salimkhani, Kian (2019) Explaining Unification in Physics Internally. Synthese. ISSN 1573-0964
2019年11月21日 星期四 下午6:09 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Gao, Shan (2019) Does the PBR theorem refute Bohmian mechanics? [Preprint]
2019年11月21日 星期四 下午6:00 | Marco Túlio Quintino, Qingxiuxiong Dong, Atsushi Shimbo, Akihito Soeda, and Mio Murao | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Marco Túlio Quintino, Qingxiuxiong Dong, Atsushi Shimbo, Akihito Soeda, and Mio Murao

Given a quantum gate implementing a d-dimensional unitary operation Ud, without any specific description but d, and permitted to use k times, we present a universal probabilistic heralded quantum circuit that implements the exact inverse Ud−1, whose failure probability decays exponentially in k. The…

[Phys. Rev. Lett. 123, 210502] Published Thu Nov 21, 2019

2019年11月21日 星期四 上午8:00 | Latest Results for Foundations of Physics

Abstract

Spin is a fundamental and distinctive property of the electron, having far-reaching implications. Yet its purely formal treatment often blurs the physical content and meaning of the spin operator and associated observables. In this work we propose to advance in disclosing the meaning behind the formalism, by first recalling some basic facts about the one-particle spin operator. Consistently informed by and in line with the quantum formalism, we then proceed to analyse in detail the spin projection operator correlation function \(C_{Q}(\varvec{a},\varvec{b})=\left\langle \left( \hat{\varvec{\sigma }}\cdot \varvec{a}\right) \left( \hat{\varvec{\sigma }}\cdot \varvec{b}\right) \right\rangle \) for the bipartite singlet state, and show it to be amenable to an unequivocal probabilistic reading. In particular, the calculation of \(C_{Q}(\varvec{a},\varvec{b})\) entails a partitioning of the probability space, which is dependent on the directions \((\varvec{a},\varvec{b}).\) The derivation of the CHSH- or other Bell-type inequalities, on the other hand, does not consider such partitioning. This observation puts into question the applicability of Bell-type inequalities to the bipartite singlet spin state.

2019年11月18日 星期一 上午7:32 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Kryukov, Alexey (2019) The classical and the quantum. [Preprint]
2019年11月18日 星期一 上午7:31 | Philsci-Archive: No conditions. Results ordered -Date Deposited.
Johns, Oliver Davis (2019) A Quantitative Version of Feynman’s Static Field Momentum Example. [Preprint]

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