# Weekly Papers on Quantum Foundations (47)

Predictability, Distinguishability and Entanglement. (arXiv:2011.08210v1 [quant-ph])

Recent times have seen a spurt of research activity focused on “completing” certain wave-particle duality relations using entanglement or polarization. These studies use a duality relation involving path-predictability, and not path-distinguishability. Quantum origins of these results are explored here, in the more general framework of multipath quantum interference. Multipath interference with a path-detector is theoretically analyzed to find the connection between predictability and distinguishability. It is shown that entanglement is what quantitatively connects distinguishability with predictability. Thus, a duality relation between distinguishability and coherence, can also be viewed as a triality between predictability, entanglement and coherence. There exist two different kind of duality relations in the literature, which pertain to two different kinds of interference experiments, with or without a path-detector. Results of this study show that the two duality relations are quantitatively connected via entanglement. The roots of the new results in the classical optical domain, including the polarization coherence theorem, can be understood in the light of this work. Additionally, the triality relations obtained can quantify wave-particle duality in the interesting case of a quanton with an internal degree of freedom. The relations can also be employed to experimentally determine the degree of bipartite entanglement.

Tsirelson’s Bound and the Quantum Monogamy Bound from Global Determinism. (arXiv:2011.08284v1 [quant-ph])

We demonstrate that in a globally deterministic universe, all spatiotemporally symmetric processes must obey counterfactual parameter independence. We show that the Tsirelson bound can be derived from counterfactual parameter independence. We show that the quantum monogamy bound can also be obtained from global determinism, and then then use these results to propose a novel solution to the horizon problem. We also explain how global determinism relates to contextuality in quantum mechanics.

Single-particle entanglement: Quantum nonlocality or quantum contextuality?. (arXiv:2011.08286v1 [quant-ph])

In 1927, at the Solvay conference, Einstein posed a thought experiment with the primary intention of showing the incompleteness of quantum mechanics; to prove it, he uses the instantaneous nonlocal effects caused by the collapse of the wave function of a single particle -the spooky action at a distance-, when a measurement is done. This historical event precede the well-know Einstein-Podolsk-Rosen criticism over the incompleteness of quantum mechanics. Here, by using the Stern-Gerlach experiment (SGE), we demonstrate how the instantaneous nonlocal feature of the collapse of the wave function together with the single-particle entanglement can be used to produce the nonlocal effect of steering. In the steering process Bob gets a quantum state depending on which observable Alice decides to measure. To accomplish this, we fully exploit the spreading (over large distances) of the entangled wave function of the single-particle. In particular, we demonstrate that the nonlocality of the single-particle entanglement allows the particle to know which detector Alice is using to steer Bob’s state. Therefore, notwithstanding strong counterarguments, we prove that the single-particle entanglement gives rise to truly nonlocal effects at two far a away places. This open the possibility of using the single-particle entanglement for implementing truly nonlocal task.

Are temporal quantum correlations generally non-monogamous?. (arXiv:2011.08437v1 [quant-ph])

In this paper we focus on the underlying quantum structure of temporal correlations and show their peculiar nature which differentiate them from spatial quantum correlations. We show rigorously that a particular entangled history, which can be associated with a quantum propagator, is monogamous to conserve its consistency throughout time. Yet evolving systems violate monogamous Bell-like multi-time inequalities. This dichotomy, being a novel feature of temporal correlations, has its roots in the measurement process itself which is discussed by means of the bundles of entangled histories. We introduce and discuss a concept of a probabilistic mixture of quantum processes by means of which we clarify why the spatial-like Bell-type monogamous inequalities are further violated. We prove that Tsirelson bound on temporal Bell-like inequalities can be derived from the entangled histories approach and as a generalization, we derive the quantum bound for multi-time Bell-like inequalities. It is also pointed out that what mimics violation of monogamy of temporal entanglement is actually just a kind of polyamory in time but monogamy of entanglement for a particular evolution still holds.

Testing Dissipative Collapse Models with a Levitated Micromagnet. (arXiv:2008.06245v2 [quant-ph] UPDATED)

We present experimental tests of dissipative extensions of spontaneous wave function collapse models based on a levitated micromagnet with ultralow dissipation. The spherical micromagnet, with radius $R=27$ $\mu$m, is levitated by Meissner effect in a lead trap at $4.2$ K and its motion is detected by a SQUID. We perform accurate ringdown measurements on the vertical translational mode with frequency $57$ Hz, and infer the residual damping at vanishing pressure $\gamma/2\pi<9$ $\mu$Hz. From this upper limit we derive improved bounds on the dissipative versions of the CSL (continuous spontaneous localization) and the DP (Di\'{o}si-Penrose) models with proper choices of the reference mass. In particular, dissipative models give rise to an intrinsic damping of an isolated system with the effect parameterized by a temperature constant; the dissipative CSL model with temperatures below 1 nK is ruled out, while the dissipative DP model is excluded for temperatures below $10^{-13}$ K. Furthermore, we present the first bounds on dissipative effects in a more recent model, which relates the wave function collapse to fluctuations of a generalized complex-valued spacetime metric.

Epistemic Horizons: This Sentence is $\frac{1}{\sqrt{2}}(|True\rangle + |False\rangle)$. (arXiv:2007.14909v2 [quant-ph] UPDATED)

Authors: Jochen Szangolies

In [Found. Phys. 48.12 (2018): 1669], the notion of ‘epistemic horizon’ was introduced as an explanation for many of the puzzling features of quantum mechanics. There, it was shown that Lawvere’s theorem, which forms the categorical backdrop to phenomena such as G\”odelian incompleteness, Turing undecidability, Russell’s paradox and others, applied to a measurement context, yields bounds on the maximum knowledge that can be obtained about a system, which produces many paradigmatically quantum phenomena. We give a brief presentation of the framework, and then demonstrate how it naturally yields Bell inequality violations. We then study the argument due to Einstein, Podolsky, and Rosen, and show how the counterfactual inference needed to conclude the incompleteness of the quantum formalism is barred by the epistemic horizon. Similarly, the paradoxes due to Hardy and Frauchiger-Renner are discussed, and found to turn on an inconsistent combination of information from incompatible contexts.

The Unruh effect in slow motion. (arXiv:2011.08223v1 [quant-ph])

We show under what conditions an accelerated detector (e.g., an atom/ion/molecule) thermalizes while interacting with the vacuum state of a quantum field in a setup where the detector’s acceleration alternates sign across multiple optical cavities. We show (non-perturbatively) in what regimes the probe `forgets’ that it is traversing cavities and thermalizes to a temperature proportional to its acceleration. Then we analyze in detail how this thermalization relates to the renowned Unruh effect. Finally, we use these results to propose an experimental testbed for the direct detection of the Unruh effect at relatively low probe speeds and accelerations, potentially orders of magnitude below previous proposals.

Weighing the Vacuum Energy. (arXiv:2011.08231v1 [hep-th])

We discuss the weight of vacuum energy in various contexts. First, we compute the vacuum energy for flat spacetimes of the form $\mathbb{T}^3 \times \mathbb{R}$, where $\mathbb{T}^3$ stands for a general 3-torus. We discover a quite simple relationship between energy at radius $R$ and energy at radius ${l_s^2\over R}$. Then we consider quantum gravity effects in the vacuum energy of a scalar field in $\mathbb{M}_3 \times S^1$ where $\mathbb{M}_3$ is a general curved spacetime. We compute it for General Relativity and generic transverse {\em TDiff} theories. In the particular case of Unimodular Gravity vacuum energy does not gravitate.

Gravitational decoherence of photons. (arXiv:2011.08270v1 [gr-qc])

Models of gravitational decoherence are not commonly applied to ultra-relativistic systems, including photons. As a result, few quantum optical tests of gravitational decoherence have been developed. In this paper, we generalize the gravitational decoherence model of Anastopoulos and Hu (arXiv:1305.5231 [gr-qc]) to photons. In this model, decoherence originates from a bath of stochastic gravitational perturbations, possibly of fundamental origin. We derive a master equation for general states of the electromagnetic (EM) field; the only free parameter is a noise temperature $\Theta$ of the gravitational fluctuations. We find that interference experiments with long baselines, accessible in near-future experiments, can, in principle, lead to strong constraints in $\Theta$.

From the Black Hole Conundrum to the Structure of Quantum Gravity. (arXiv:2011.08707v1 [hep-th])

Authors: Yasunori Nomura

We portray the structure of quantum gravity emerging from recent progress in understanding the quantum mechanics of an evaporating black hole. Quantum gravity admits two different descriptions, based on Euclidean gravitational path integral and a unitarily evolving holographic quantum system, which appear to present vastly different pictures under the existence of a black hole. Nevertheless, these two descriptions are physically equivalent. Various issues of black hole physics—including the existence of the interior, unitarity of the evolution, the puzzle of too large interior volume, and the ensemble nature seen in certain calculations—are addressed very differently in the two descriptions, still leading to the same physical conclusions. The perspective of quantum gravity developed here is expected to have broader implications beyond black hole physics, especially for the cosmology of the eternally inflating multiverse.

Models of Discrete Linear Evolution for Quantum Systems. (arXiv:2011.08715v1 [gr-qc])

Authors: Jakub Káninský

Discrete canonical evolution is a key tool for understanding the dynamics in discrete models of spacetime, in particular those represented by a triangular Regge lattice. We consider a finite-dimensional system whose evolution is realized by a series of discrete-time evolution steps governed by Hamiltonian equations of motion that are linear in the canonical coordinates. The evolution is allowed to be irregular, which produces constraints as well as non-uniqueness of solutions. We provide two independent and fundamentally different approaches to canonical quantization of this system, including detailed description of the evolution maps, measurement and path integrals. It is argued that some irregular discrete systems may be most naturally described by a non-unitary quantum evolution. The formalism is then applied to a simple yet physically relevant model of massless scalar field on a two-dimensional spacetime lattice.

Testing and Emulating Modified Gravity on Cosmological Scales. (arXiv:2011.08786v1 [astro-ph.CO])

Authors: Andrius Tamosiunas

This thesis introduces a set of methods for testing models of modified gravity using galaxy clusters. In particular, a technique for constraining models with a chameleon screening is introduced. In addition, the outlined technique is expanded to test a wider class of models, such as the theory of emergent gravity. Finally, the first part of the thesis is concluded by adapting the mentioned tests for model independent constraints. The obtained results indicate that galaxy clusters can be used to obtain some of the most powerful constraints on cosmological scales.

The second part of the thesis is dedicated to the topic of cosmological emulators. More specifically, a technique of emulating cosmological N-body simulation output data based on machine learning is introduced. Generative adversarial networks (GANs) are used to emulate dark matter-only as well as hydrodynamical simulation data. In addition, N-body modified gravity simulations are explored as well. The presented investigation of the GAN algorithm shows that such emulators offer a powerful, fast and efficient way of producing simulation output data with different cosmological parameters. The power spectrum analysis indicates a 1-20% difference between the training and the generated data depending on the dataset used and whether Gaussian smoothing is applied or not.

Probing the scale of grand unification with gravitational waves. (arXiv:1912.03695v2 [hep-ph] UPDATED)

The spontaneous breaking of U(1)_B-L around the scale of grand unification can simultaneously account for hybrid inflation, leptogenesis, and neutralino dark matter, thus resolving three major puzzles of particle physics and cosmology in a single predictive framework. The B-L phase transition also results in a network of cosmic strings. If strong and electroweak interactions are unified in an SO(10) gauge group, containing U(1)_B-L as a subgroup, these strings are metastable. In this case, they produce a stochastic background of gravitational waves that evades current pulsar timing bounds, but features a flat spectrum with amplitude h^2\Omega_GW ~ 10^-8 at interferometer frequencies. Ongoing and future LIGO observations will hence probe the scale of B-L breaking.

On how Epistemological Letters changed the foundations of quantum mechanics

Murgueitio Ramírez, Sebastián (2020) On how Epistemological Letters changed the foundations of quantum mechanics. [Preprint]

Free Will and the Cross-Level Consequence Argument

Birch, Jonathan (2020) Free Will and the Cross-Level Consequence Argument. [Preprint]

Structural Realism and Generative Grammar

Nefdt, Ryan M. (2020) Structural Realism and Generative Grammar. [Preprint]

The ontology of a theory

Cocco, Lorenzo (2020) The ontology of a theory. [Preprint]

No relation for Wigner’s friend

Castellani, Leonardo (2020) No relation for Wigner’s friend. [Preprint]

Three noncontextual hidden variable models for the Peres-Mermin square

Gábor, Hofer-Szabó (2020) Three noncontextual hidden variable models for the Peres-Mermin square. [Preprint]

Constitutive Elements Through Perspectival Lenses

Sanjuán, Mariano (2020) Constitutive Elements Through Perspectival Lenses. [Preprint]

Hamilton, Hamiltonian Mechanics, and Causation

Weaver, Christopher (2020) Hamilton, Hamiltonian Mechanics, and Causation. [Preprint]

How uncertainty can save measurement from circularity and holism

Ritson, Sophie and Staley, Kent (2020) How uncertainty can save measurement from circularity and holism. Studies in History and Philosophy of Science Part A. ISSN 00393681

Minimizing Backaction through Entangled Measurements

Author(s): Kang-Da Wu, Elisa Bäumer, Jun-Feng Tang, Karen V. Hovhannisyan, Martí Perarnau-Llobet, Guo-Yong Xiang, Chuan-Feng Li, and Guang-Can Guo

When an observable is measured on an evolving coherent quantum system twice, the first measurement generally alters the statistics of the second one, which is known as measurement backaction. We introduce, and push to its theoretical and experimental limits, a novel method of backaction evasion, whe…

[Phys. Rev. Lett. 125, 210401] Published Mon Nov 16, 2020

A solid look at molecules

Nature Physics, Published online: 16 November 2020; doi:10.1038/s41567-020-01080-4

When molecular model systems, such as polycyclic aromatic hydrocarbons, are ionized by ultrashort extreme ultraviolet pulses, their relaxation path proceeds via electron–phonon scattering, linking molecules to typical solid-state matter behaviour.

Two dogmas of dynamicism

Abstract

I critically discuss two dogmas of the “dynamical approach” to spacetime in general relativity, as advanced by Harvey Brown [Physical Relativity (2005) Oxford:Oxford University Press] and collaborators. The first dogma is that positing a “spacetime geometry” has no implications for the behavior of matter. The second dogma is that postulating the “Strong Equivalence Principle” suffices to ensure that matter is “adapted” to spacetime geometry. I conclude by discussing “spacetime functionalism”. The discussion is presented in reaction to and sympathy with recent work by James Read [“Explanation, geometry, and conspiracy in relativity theory” (2020) Thinking about Spacetime Boston: Birkäuser].

Explanatory Games

Mantzavinos, C. (2013) Explanatory Games. The Journal of Philosophy, CX. pp. 606-632. ISSN 0022-362X