# Weekly Papers on Quantum Foundations (37)

Parity-Time Symmetry via Time-Dependent non-Unitary Gauge Fields. (arXiv:2109.03846v1 [physics.class-ph])

Parity-Time (PT) symmetric systems have been widely recognized as fundamental building blocks for the development of novel, ultra-sensitive opto-electronic devices. However, arguably one of their major drawbacks is that they rely on non-linear amplification processes that could limit their potential applications, particularly in the quantum realm. In this work, we show both theoretically and experimentally that gain-loss, PT-symmetric systems can be designed by means of linear, time-modulated components. More specifically, by making use of a state-of-the-art, fully reconfigurable electronic platform, we demonstrate that PT-symmetry breaking transitions can be observed by properly modulating the inductance (L) and the capacitance (C) of a single LC circuit. Importantly, the lossless dynamic-variations of the electrical components used in our LC circuits allow us to control the static and periodic (Floquet) regimes of our PT-symmetric system. Our results challenge the conventional wisdom that at least two-oscillator systems are needed for observing PT-symmetric phenomena, and provide a new perspective in the field of synthetic PT symmetry with important implications for sensing, energy transfer and topology.

Violation $\neq$ Quantum. (arXiv:2109.03871v1 [quant-ph])

The only entanglement quantity is concurrence in a 2-qubit pure state. The maximum violation of Bell’s inequality is monotonically increasing for this quantity. Therefore, people expect that pure state entanglement is relevant to the quantum violation. To understand the relation between violation and entanglement, we extend the study to three qubits. We consider all possible 3-qubit operators with a symmetric permutation. When only turning on one entanglement measure, the numerical result shows a contradiction to the expectation. The maximum violation does not have the same behavior as in 2-qubit pure states. Therefore, we conclude “Violation$\neq$Quantum”. In the end, we propose the generalized $R$-matrix or correlation matrix for the new diagnosis of Quantum Entanglement. We demonstrate the evidence by restoring the monotonically increasing result.

Spooky action at a distance also acts in the past. (arXiv:2109.04151v1 [quant-ph])

The term `spooky action at a distance’ was coined by A. Einstein to show inconsistency of quantum mechanics with the principle of locality and reality. However, quantum mechanics is nonlocal and violates Bell’s inequality. A quantum state measurement of a particle of an entangled pair collapses the total quantum state and the quantum state of the distant particle is immediately determined without making any interaction with it. The isolated collapsed quantum state of both particles remains unentangled in the future. An inertial frame of reference moving with a relativistic speed perceives these events differently is space and time and their simultaneity is relative. In this paper, it is shown that the quantum state collapse happens not only in the present but it also happens in the past of the collapse event.

Entanglement and superposition are equivalent concepts in any physical theory. (arXiv:2109.04446v1 [quant-ph])

We prove that any two general probabilistic theories (GPTs) are entangleable, in the sense that their composite exhibits either entangled states or entangled measurements, if and only if they are both non-classical, meaning that neither of the state spaces is a simplex. This establishes the universal equivalence of the (local) superposition principle and the existence of global entanglement, valid in a fully theory-independent way. As an application of our techniques, we show that all non-classical GPTs exhibit a strong form of incompatibility of states and measurements, and use this to construct a version of the BB84 protocol that works in any non-classical GPT.

General Relativity’s energy and positivity — a brief history. (arXiv:2109.03936v1 [physics.hist-ph])

Authors: S.Deser

I give a brief review of the search for a proper definition of energy in General Relativity (GR), a far from trivial quest, which was only completed after four and a half decades. The equally (or perhaps more) difficult task of establishing its positivity — it was to take another fifteen plus years — will then be summarized. Extension to cosmological GR is included. Mention is made of some recent offshoots.

Chaos-protected locality. (arXiv:2109.03825v1 [quant-ph])

Authors: Shao-Kai JianBrian Swingle

Microscopic speed limits that constrain the motion of matter, energy, and information abound in physics, from the “ultimate” speed limit set by light to Lieb-Robinson speed limits in quantum spin systems. In addition to these state-independent speed limits, systems can also be governed by emergent state-dependent speed limits indicating slow dynamics arising, for example, from slow low-energy quasiparticles. Here we describe a different kind of speed limit: a situation where complex information/entanglement spreads rapidly, in a fashion inconsistent with any speed limit, but where simple signals continue to obey an approximate speed limit. If we take the point of view that the motion of simple signals defines the local spacetime geometry of the universe, then the effects we describe show that spacetime locality can be compatible with a high degree of non-local interactions provided these are sufficiently chaotic. With this perspective, we sharpen a puzzle about black holes recently raised by Shor and propose a schematic resolution.

What actually happens when you approach a gravitational singularity?. (arXiv:2109.04061v1 [gr-qc])

Authors: Susan M. ScottBen E. Whale

Roger Penrose’s 2020 Nobel Prize in Physics recognises that his identification of the concepts of “gravitational singularity” and an “incomplete, inextendible, null geodesic” is physically very important. The existence of an incomplete, inextendible, null geodesic doesn’t say much, however, if anything, about curvature divergence, nor is it a helpful definition for performing actual calculations. Physicists have long sought for a coordinate independent method of defining where a singularity is located, given an incomplete, inextendible, null geodesic, that also allows for standard analytic techniques to be implemented. In this essay we present a solution to this issue. It is now possible to give a concrete relationship between an incomplete, inextendible, null geodesic and a gravitational singularity, and to study any possible curvature divergence using standard techniques.

Dark Energy and the Time Dependence of Fundamental Particle Constants. (arXiv:2103.09622v2 [hep-ph] UPDATED)

Authors: Bodo Lampe

The cosmic time dependencies of $G$, $\alpha$, $\hbar$ and of Standard Model parameters like the Higgs vev and elementary particle masses are studied in the framework of a new dark energy interpretation. Due to the associated time variation of rulers, many effects turn out to be invisible. However, a rather large time dependence is claimed to arise in association with dark energy measurements, and smaller ones in connection with the Standard Model.

Hilbert-Style Axiomatic Completion: The (Not So) Hidden Contextuality of von Neumann’s “No Hidden Variables” Theorem

Mitsch, Chris (2021) Hilbert-Style Axiomatic Completion: The (Not So) Hidden Contextuality of von Neumann’s “No Hidden Variables” Theorem. [Preprint]

Quantum Theory Cannot Violate a Causal Inequality

Author(s): Tom Purves and Anthony J. Short

Within quantum theory, we can create superpositions of different causal orders of events, and observe interference between them. This raises the question of whether quantum theory can produce results that would be impossible to replicate with any classical causal model, thereby violating a causal in…

[Phys. Rev. Lett. 127, 110402] Published Fri Sep 10, 2021

Bipartite Measurements in Minkowski Space

King, Robbie (2021) Bipartite Measurements in Minkowski Space. [Preprint]

A. Douglas Stone. Einstein and the Quantum: The Quest of the Valiant Swabian. 332 pp. Princeton University Press, 2013.

Leifer, Matthew Saul (2016) A. Douglas Stone. Einstein and the Quantum: The Quest of the Valiant Swabian. 332 pp. Princeton University Press, 2013. Spontaneous Generations: A Journal for the History and Philosophy of Science, 8 (1). pp. 105-108. ISSN 1913-0465

Maxwellian Electrodynamics Genesis and Development: Intertheoretic Context

Nugayev, Rinat Magdievich (2016) Maxwellian Electrodynamics Genesis and Development: Intertheoretic Context. Spontaneous Generations: A Journal for the History and Philosophy of Science, 8 (1). pp. 55-92. ISSN 1913-0465

A night for science

Nature Physics, Published online: 08 September 2021; doi:10.1038/s41567-021-01362-5

The European Researchers’ Night provides a platform for scientists to engage with the public.

Even more exotic

Nature Physics, Published online: 08 September 2021; doi:10.1038/s41567-021-01353-6

Even more exotic

Interaction-Free Measurement with Electrons

Author(s): Amy E. Turner, Cameron W. Johnson, Pieter Kruit, and Benjamin J. McMorran

Here, we experimentally demonstrate interaction-free measurements with electrons using a novel electron Mach-Zehnder interferometer. The flexible two-grating electron interferometer is constructed in a conventional transmission electron microscope and achieves high contrast in discrete output detect…

[Phys. Rev. Lett. 127, 110401] Published Tue Sep 07, 2021

Four-dimensionalism, eternalism, and deprivationist accounts of the evil of death

Abstract

Four-dimensionalists think that we persist over time by having different temporal parts at each of the times at which we exist. Eternalists think that all times are equally real. Deprivationists think that death is an evil for the one who dies because it deprives them of something. I argue that four-dimensionalist eternalism, conjoined with a standard deprivationist account of the evil of death, has surprising implications for what we should think about the evil of death. In particular, given these assumptions, we will lack any grounds for thinking that death is an evil for some individuals for whom we would antecedently expect it to be an evil, namely those individuals who cease to exist at death. Alternatively, we will only have some grounds for thinking that death is an evil for certain individuals for whom we might antecedently be more inclined to think death is not an evil, namely those individuals who survive death, in the sense that they continue to exist after death.