# Weekly Papers on Quantum Foundations (6)

Quantum Metaphysics and the Foundations of Spacetime

Lam, Vincent and Letertre, Laurie and Mariani, Cristian (2022) Quantum Metaphysics and the Foundations of Spacetime. [Preprint]

The role of idealisations in describing an isolated molecule

Seifert, Vanessa A. (2019) The role of idealisations in describing an isolated molecule. Foundations of Chemistry. pp. 15-29. ISSN 1386-4238

The Information-Theoretic View of Quantum Mechanics and the Measurement Problem(s)

Laudisa, Federico (2022) The Information-Theoretic View of Quantum Mechanics and the Measurement Problem(s). [Preprint]

Theorems motivated by foundations of quantum mechanics and some of their applications. (arXiv:2202.01304v1 [quant-ph])

This paper provides theorems aimed at shedding light on issues in the foundations of quantum mechanics. These theorems can be used to propose new interpretations to the theory, or to better understand, evaluate and improve current interpretations. Some of these applications include: (1) A proof of the existence of pilot-wave theories that are fully equivalent to standard quantum mechanics in a path-wise sense. This equivalence is stronger than what is entailed from the more traditional requirements of equivariance, or good mixing properties, and is necessary to assure proper correlations across time and proper records of the past. (2) A proposal for a minimalistic ontology for non-collapse quantum mechanics, in which Born’s rule provides the proper predictions.(3) The observation of a close relationship between Born’s rule and a version of the superposition principle.

How the Many Worlds Interpretation brings Common Sense to Paradoxical Quantum Experiments. (arXiv:2202.01438v1 [quant-ph])

The many worlds interpretation of quantum mechanics (MWI) states that the world we live in is just one among many parallel worlds. It is widely believed that because of this commitment to parallel worlds, the MWI violates common sense. Some go so far as to reject the MWI on this basis. This is despite its myriad of advantages to physics (e.g. consistency with relativity theory, mathematical simplicity, realism, determinism, etc.). Here, we make the case that common sense in fact favors the MWI. We argue that causal explanations are commonsensical only when they are local causal explanations. We present several quantum mechanical experiments that seem to exhibit nonlocal “action at a distance”. Under the assumption that only one world exists, these experiments seem immune to local causal explanation. However, we show that the MWI, by taking all worlds together, can provide local causal explanations of the experiments. The MWI therefore restores common sense to physical explanation.

A covariant non-local phase field model of Bohm’s potential. (arXiv:2202.01533v1 [quant-ph])

Assuming that the energy of a gas depends non-locally on the logarithm of its mass density, the body force in the resulting equation of motion consists of the sum of density gradient terms. Truncating this series after the second term, Bohm’s quantum potential and the Madelung equations are obtained, showing explicitly that some of the hypotheses that led to the formulationb of quantum mechanics do admit a classical interpretation based on non-locality. Here, we generalize this approach imposing a finite speed of propagation of any perturbation, thus determining a covariant formulation of the Madelung equation.

Tests of physics beyond the Standard Model with single-electron ions. (arXiv:2202.01668v1 [physics.atom-ph])

A highly effective approach to the search for hypothetical new interactions through isotope shift spectroscopy of hydrogen-like ions is presented. A weighted difference of the g factor and ground-state energy is shown to assist in the suppression of detrimental uncertainties from nuclear structure, while preserving the hypothetical contributions from new interactions. Experimental data from only a single isotope pair is required. Account is taken of the small, subleading nuclear corrections, allowing to show that, provided feasible experimental progress is achieved in UV/X-ray spectroscopy, the presented approach can yield competitive bounds on New Physics electron coupling parameters improved by more than an order of magnitude compared to leading bounds from atomic physics.

Edge modes as reference frames and boundary actions from post-selection. (arXiv:2109.06184v4 [hep-th] UPDATED)

We introduce a general framework realizing edge modes in (classical) gauge field theory as dynamical reference frames, an often suggested interpretation that we make entirely explicit. We focus on a bounded region $M$ with a co-dimension one time-like boundary $\Gamma$, which we embed in a global spacetime. Taking as input a variational principle at the global level, we develop a systematic formalism inducing consistent variational principles (and in particular, boundary actions) for the subregion $M$. This relies on a post-selection procedure on $\Gamma$, which isolates the subsector of the global theory compatible with a general choice of gauge-invariant boundary conditions for the dynamics in $M$. Crucially, the latter relate the configuration fields on $\Gamma$ to a dynamical frame field carrying information about the spacetime complement of $M$; as such, they may be equivalently interpreted as frame-dressed or relational observables. Generically, the external frame field keeps an imprint on the ensuing dynamics for subregion $M$, where it materializes itself as a local field on the time-like boundary $\Gamma$; in other words, an edge mode. We identify boundary symmetries as frame reorientations and show that they divide into three types, depending on the boundary conditions, that affect the physical status of the edge modes. Our construction relies on the covariant phase space formalism, and is in principle applicable to any gauge (field) theory. We illustrate it on three standard examples: Maxwell, Abelian Chern-Simons and non-Abelian Yang-Mills theories. In complement, we also analyze a mechanical toy-model to connect our work with recent efforts on (quantum) reference frames.

Interferometry of black holes with Hawking radiation. (arXiv:2109.07044v3 [gr-qc] UPDATED)

We investigate the wave optical imaging of black holes with Hawking radiation. The spatial correlation function of Hawking radiation is expressed in terms of transmission and reflection coefficients for scalar wave modes and evaluated by numerically summing over angular quantum numbers for the Unruh-Hawking state of the Kerr-de Sitter black hole. Then, wave optical images of an evaporating black hole are obtained by the Fourier transformation of the spatial correlation function. For short wavelength, the image of the black hole with the outgoing mode of the Unruh-Hawking state has the appearance of a star with its surface given by the photon sphere. It is found that interference between incoming modes from the cosmological horizon and reflected modes due to the scattering of the black hole can enhance brightness of images in the vicinity of the photon sphere. For a long wavelength, the entire field of view is bright, and the emission region of Hawking radiation cannot be identified.

Qubit clock in quantum cosmology. (arXiv:2201.02770v2 [gr-qc] UPDATED)

We investigate the emergent time scenario in quantum cosmology based on the Page-Wotters approach. Using a quantum cosmological model with a qubit clock, it is demonstrated how the entanglement between the qubit clock and the geometry derives emergence of a time parameter which defines evolution of the timeless quantum state of the universe. We show the universe wave function conditioned by a qubit clock obeys the standard Schr\”{o}dinger equation and the Fisher information for the clock state, which quantifies entanglement between the universe and the clock, contributes as a negative energy density.

Mechanism for the quantum natured gravitons to entangle masses. (arXiv:2201.03583v2 [gr-qc] UPDATED)

This paper points out the importance of the quantum nature of the gravitational interaction with matter in a linearized theory of quantum gravity induced entanglement of masses (QGEM). We will show how the quantum interaction entangles the steady states of a closed system (eigenstates) of two test masses placed in the harmonic traps, and how such a quantum matter-matter interaction emerges from an underlying quantum gravitational field. We will rely upon quantum perturbation theory highlighting the critical assumptions for generating a quantum matter-matter interaction and showing that a classical gravitational field does not render such an entanglement. We will consider two distinct examples; one where the two harmonic oscillators are static and interact via an exchange of a virtual spin-2 and spin-0 components of the graviton, and the other where the harmonic oscillators are non-static and interact with a virtual graviton corresponding to the gravitational wave beside the static components of the graviton propagator. The quantum nature of the gravitons interacting with the harmonic oscillators are responsible for creating an entangled state with the ground and the excited states of harmonic oscillators as the Schmidt basis. We will compute the concurrence as a criterion for the above entanglement and compare the two ways of entangling the two harmonic oscillators.

Direct measurement of particle statistical phase. (arXiv:2202.00575v2 [quant-ph] UPDATED)

The symmetrization postulate in quantum mechanics is formally reflected in the appearance of an exchange phase ruling the symmetry of identical particle global states under particle swapping. Many indirect measurements of this fundamental phase have been reported so far, while a direct observation has been only recently achieved for photons. Here we propose a general scheme capable to directly measure the exchange phase of any type of particles (bosons, fermions, anyons), exploiting the operational framework of spatially localized operations and classical communication. We experimentally implement it in an all-optical platform providing proof-of-principle for different simulated exchange phases. As a byproduct, we supply a direct measurement of the real bosonic exchange phase of photons. Also, we analyze the performance of the proposed scheme when mixtures of particles of different nature are injected. Our results confirm the symmetrization tenet and provide a tool to explore it in various scenarios.

Sifting quantum black holes through the principle of least action. (arXiv:2202.01216v1 [hep-th])

Authors: Benjamin KnorrAlessia Platania

We tackle the question of whether known regular black holes or other alternatives to the Schwarzschild solution can arise from an action principle in quantum gravity. Focusing on an asymptotic expansion of such solutions and inspecting the corresponding field equations, we demonstrate that their realization within a principle of stationary action would require either fine-tuning, or large-distance non-localities of the Polyakov type, whose specific coefficients imply a vanishing graviton two-point function in Minkowski space. This points to an incompatibility between a local action principle in quantum gravity and many of the known alternatives to classical black holes.

Observational constraints on varying fundamental constants in a minimal CPC Model. (arXiv:2202.01371v1 [gr-qc])

A minimal model based on the Covariant Physical Couplings (CPC) framework for gravity is proposed. The CPC framework is based on the assumptions of a metric-compatible four-dimensional Riemannian manifold where a covariantly conserved stress-energy tensor acts as source of the field equations which are formally the same as Einstein field equations, but where the couplings $\{ G, c,\Lambda \}$ are allowed to vary simultaneously. The minimal CPC model takes $\Lambda$ as a genuine constant while $c$ and $G$ vary in an entangled way that is consistent with Bianchi identity and the aforementioned assumptions. The model is constrained using the most recent galaxy cluster gas mass fraction observational data. Our result indicates that the functions $c(z)$ and $G\left(z\right)=G_{0}\left(c/c_{0}\right)^{4}$ are compatible with constant couplings for the two different parameterizations of $c=c(z)$ adopted here.

Lost in translation: the Abelian affine connection (in the coincident gauge). (arXiv:2202.01701v1 [gr-qc])

Authors: Jose Beltrán JiménezTomi S. Koivisto

The simplest i.e. the Abelian i.e. the commutative i.e. the integrable i.e. the flat and torsion-free i.e. the symmetric teleparallel affine connection has been considered in many recent works in the literature. Such an affine connection is characterised by the property that it can be vanished by a general coordinate transformation, by fixing the so called coincident gauge. This article focuses on the subtleties involved in the applications of the coincident gauge.

Carroll Expansion of General Relativity. (arXiv:2112.12684v2 [hep-th] UPDATED)

We study the small speed of light expansion of general relativity, utilizing the modern perspective on non-Lorentzian geometry. This is an expansion around the ultra-local Carroll limit, in which light cones close up. To this end, we first rewrite the Einstein-Hilbert action in pre-ultra-local variables, which is closely related to the 3+1 decomposition of general relativity. At leading order in the expansion, these pre-ultra-local variables yield Carroll geometry and the resulting action describes the electric Carroll limit of general relativity. We also obtain the next-to-leading order action in terms of Carroll geometry and next-to-leading order geometric fields. The leading order theory yields constraint and evolution equations, and we can solve the evolution analytically. We furthermore construct a Carroll version of Bowen-York initial data, which has associated conserved boundary linear and angular momentum charges. The notion of mass is not present at leading order and only enters at next-to-leading order. This is illustrated by considering a particular truncation of the next-to-leading order action, corresponding to the magnetic Carroll limit, where we find a solution that describes the Carroll limit of a Schwarzschild black hole. Finally, we comment on how a cosmological constant can be incorporated in our analysis.

Experimental Verification of Dissipation-Time Uncertainty Relation

Author(s): L.-L. Yan, J.-W. Zhang, M.-R. Yun, J.-C. Li, G.-Y. Ding, J.-F. Wei, J.-T. Bu, B. Wang, L. Chen, S.-L. Su, F. Zhou, Y. Jia, E.-J. Liang, and M. Feng

Experiments with a single calcium atom prove that processes of change have a speed limit determined by the rate at which they can dissipate heat.

[Phys. Rev. Lett. 128, 050603] Published Fri Feb 04, 2022

On the ontological status of molecular structure: is it possible to reconcile molecular chemistry with quantum mechanics?

Fortin, Sebastian and Labarca, Martín and Lombardi, Olimpia (2022) On the ontological status of molecular structure: is it possible to reconcile molecular chemistry with quantum mechanics? [Preprint]

Truth and reality: How to be a scientific realist without believing scientific theories should be true

Potochnik, Angela (2022) Truth and reality: How to be a scientific realist without believing scientific theories should be true. [Preprint]

There is Cause to Randomize

Larroulet Philippi, Cristian (2022) There is Cause to Randomize. Philosophy of Science, 89 (1). pp. 152-170.

Relational Quantum Cosmology

Vidotto, Francesca (2015) Relational Quantum Cosmology. Philosophy of Cosmology. pp. 297-316.

The relational ontology of contemporary physics

Vidotto, Francesca (2022) The relational ontology of contemporary physics. [Preprint]

[Preprint]Lombardi, Olimpia and Fortin, Sebastian and Pasqualini, Matias (2022) Possibility and time in quantum mechanics.

[Preprint]Carcassi, Gabriele and Oldofredi, Andrea and Aidala, Christine A (2022) On the reality of the quantum state once again.

[Preprint]Arvan, Marcus and Bright, Liam Kofi and Heesen, [Preprint]Martinez, Marco and Teira, David (2022) Why Experimental Balance is Still a Reason to Randomize.

[Preprint]Gao, Shan (2022) Why the quantum equilibrium hypothesis? From Bohmian mechanics to a many-worlds theory. [Preprint]