# Weekly Papers on Quantum Foundations (18)

A local hidden-variable model for experimental tests of the GHZ puzzle. (arXiv:2104.14503v1 [quant-ph])

The Greenberger-Horne-Zeilinger (GHZ) puzzle has been used to study quantum nonlocality and provide an all-or-nothing, no-go theorem for local hidden-variable models. Recent experiments using coincident-detected entangled photons prepared in a three-particle GHZ state have been used to test quantum nonlocality, but fail to rule out local realism due to a reliance on the fair-sampling hypothesis and insufficient detection efficiency. This paper describes a physically motivated local hidden-variable model based on amplitude-threshold detection that is capable of producing similar results. Detection efficiencies for the model are within the bounds permitted for local realism and, interestingly, exhibit statistical correlations between detectors, even when the detection events are spacelike separated. Increasing the detection threshold improves agreement with the ideal quantum predictions at the cost of decreased detection efficiency. A curious emergent feature of the model is that detection efficiencies may depend upon which observables are chosen for measurement.

Genuine activation of nonlocality: From locally available to locally hidden information. (arXiv:2104.11933v2 [quant-ph] UPDATED)

Quantum nonlocality has different manifestations that, in general, are revealed by local measurements of the parts of a composite system. In this paper, we focus on the kind of nonlocality that arises from a set of orthogonal states that cannot be perfectly distinguished by local operations and classical communication (LOCC). Such a set is deemed nonlocal, for a joint measurement on the whole system is necessary for perfect discrimination of the states with certainty. On the other hand, a set of orthogonal states that can be perfectly distinguished by LOCC is believed to be devoid of nonlocal properties. In this paper, we study the properties of orthogonal sets that are locally distinguishable and without local redundancy. The latter implies that they become nonorthogonal on discarding one or more subsystems. We show that such a set may be locally converted, with certainty, into another orthogonal set of states that cannot be locally distinguished. Notably, the cardinality does not change in the process. We illustrate this with several examples. We also provide a partial characterization of those that do not have this property. Conceptually, our result can be viewed as activation of nonlocality in the scenario of local state discrimination. We also suggest an application, namely, local hiding of information, that allows us to locally hide the locally available information without losing any part. Once hidden, the information in its entirety can only be retrieved using entanglement.

A translation of G.W. Krafft’s “On a new type of oscillations”. (arXiv:2104.14505v1 [physics.hist-ph])

Authors: Sylvio R Bistafa

This is a translation from Latin of ‘De novo oscillationum genere’, which was motivated by Krafft’s accidental observation of a suspended clock setting itself in constant motion as a pendulum. This publication, in turn, motivated Euler to write ‘De novo genere oscillationum’, in which Euler derived for the first time, the differential equation for the (undamped) simple harmonic oscillator under harmonic excitation.

Cosmology from pregeometry. (arXiv:2104.14013v1 [gr-qc])

Authors: C. Wetterich

We discuss cosmological solutions for a diffeomorphism invariant gauge theory of the non-compact Lorentz group $SO(1,3)$. Besides the gauge bosons our model of pregeometry contains a vector field in the vector representation of $SO(1,3)$ and a scalar singlet. General relativity and variable gravity emerge as effective theories for large distances and times in Planck units. We propose an approximation to the effective action with up to two derivatives. For a suitable range of parameters the universe approaches for large times stable Minkowski space. For late cosmology the model predicts dynamical dark energy and provides for a candidate for dark matter. Early cosmology is characterized by an inflationary epoch. The beginning of the universe in the infinite past is great emptiness, corresponding to an ultraviolet fixed point with the associated quantum scale symmetry. The beginning universe is a vacuum state with vanishing expectation values and finite non-vanishing correlation functions for the fluctuations of all fields. There is no physical big bang singularity.

Testing $f(Q, T)$ gravity models that reduce to $\Lambda CDM$. (arXiv:2104.14065v1 [gr-qc])

Authors: Antonio NájeraAmanda Fajardo

We tested four $f(Q,T)$ models in an extension of symmetric teleparallel gravity whose Friedmann equations reduce to $\Lambda CDM$ for certain parameters. Using low-redshift data we found that all our models were 2$\sigma$ consistent with $\Lambda CDM$ and the Hubble constant value were $\sigma$ consistent with the one of the SH0ES collaboration and at $12\sigma$ tension with the one of the Planck Collaboration. To see whether one of our models can challenge $\Lambda CDM$ at a background perspective, we computed the Bayesian evidence for our four models and $\Lambda CDM$. The concordance model was preferred over all our $f(Q,T)$ alternate models, showing a weak preference against models $f(Q,T) = -Q/G_N + bT$ and $-(Q+2\Lambda)/G_N + bT$ and a substantial preference against models $f(Q,T) = -(Q+2H_0c(Q/(6H_0^2))^{n+1})/G_N + bT$ and $f(Q,T) = -(Q+2H_0c(Q/(6H_0^2))^{n+1} + 2\Lambda)/G_N + bT$. Our models were successful to reproduce $\Lambda CDM$ acceleration from low redshifts.

A Measure of Classicality. (arXiv:2104.14465v1 [gr-qc])

Authors: James B. Hartle (UCSB), Murray Gell-Mann (deceased)

A striking feature of our fundamentally indeterministic quantum universe is its quasiclassical realm — the wide range of time place and scale in which the deterministic laws of classical physics hold. Our quasiclassical realmis an emergent feature of the fundamental theories of our universe’s quantum state and dynamics. There are many types of quasiclassical realms our Universe could exhibit characterized by different variables, different levels of coarse-graining, different locations in spacetime, different classical physics, and different levels of classicality.We propose a measure of classicality for quasiclassical realms, We speculate on the observable consequences of different levels of classicality especially for information gathering and utilizing systems (IGUSes) such ourselves as observers of the Universe.

Spontaneous Lorentz violation and asymptotic flatness. (arXiv:2103.07611v2 [gr-qc] UPDATED)

Authors: Yuri BonderChristian Peterson

The Standard Model Extension (SME) is a generic parametrization for Lorentz violation and the phenomenological consequences of the minimal gravity sector of the SME are usually studied using a post-Newtonian expansion that requires spacetime to be asymptotically flat. However, there is a term in this sector for which these approximations are unable to make predictions; this is known as the $t$ puzzle. The present paper studies a model of spontaneous Lorentz violation in the minimal gravity sector of the SME in a static and spherically symmetric situation, when no additional matter fields are present. It is shown that, under the above mentioned assumptions, $t$ is the only term in the minimal gravity sector for which no asymptotically flat solutions exist. This stems from the fact that the $t$ term fixes the asymptotic behavior of all the pieces of the curvature tensor.

Beables, Primitive Ontology and Beyond: How Theories Meet the World

Oldofredi, Andrea (2021) Beables, Primitive Ontology and Beyond: How Theories Meet the World. [Preprint]

Perennial Symmetry Arguments: Aristotle’s Heavenly Cosmology and Noether’s First Theorem

Miller, Ryan (2019) Perennial Symmetry Arguments: Aristotle’s Heavenly Cosmology and Noether’s First Theorem. Proceedings of the American Catholic Philosophical Association, 93.

Must Hidden Variables Theories Be Contextual? Kochen & Specker meet von Neumann and Gleason

Acuña, Pablo (2021) Must Hidden Variables Theories Be Contextual? Kochen & Specker meet von Neumann and Gleason. European Journal for Philosophy of Science, 41. ISSN 1879-4912

The Maxim of Probabilism — with special regard to Reichenbach

Rédei, Miklós and Gyenis, Zalán (2021) The Maxim of Probabilism — with special regard to Reichenbach. [Preprint]

Learning models of quantum systems from experiments

Nature Physics, Published online: 29 April 2021; doi:10.1038/s41567-021-01201-7

Quantum systems make it challenging to determine candidate Hamiltonians from experimental data. An automated protocol is presented and its capabilities to infer the correct Hamiltonian are demonstrated in a nitrogen-vacancy centre set-up.

Atomtronic Matter-Wave Lensing

Author(s): Saurabh Pandey, Hector Mas, Georgios Vasilakis, and Wolf von Klitzing

A new “lensing” technique counters the spreading of an ultracold cloud of atoms inside a tiny waveguide.

[Phys. Rev. Lett. 126, 170402] Published Wed Apr 28, 2021

Information and Thermodynamics: Fast and Precise Approach to Landauer’s Bound in an Underdamped Micromechanical Oscillator

Author(s): Salambô Dago, Jorge Pereda, Nicolas Barros, Sergio Ciliberto, and Ludovic Bellon

The Landauer principle states that at least kBTln2 of energy is required to erase a 1-bit memory, with kBT the thermal energy of the system. We study the effects of inertia on this bound using as one-bit memory an underdamped micromechanical oscillator confined in a double-well potential created by …

[Phys. Rev. Lett. 126, 170601] Published Tue Apr 27, 2021

Preparation in Bohmian Mechanics

ROVELLI, Carlo (2021) Preparation in Bohmian Mechanics. [Preprint]

Probability and Irreversibility in Modern Statistical Mechanics: Classical and Quantum

Wallace, David (2016) Probability and Irreversibility in Modern Statistical Mechanics: Classical and Quantum. [Preprint]