# Weekly Papers on Quantum Foundations (50)

Reinterpreting the universe-multiverse debate in light of inter-model inconsistency in set theory

Kuby, Daniel (2021) Reinterpreting the universe-multiverse debate in light of inter-model inconsistency in set theory. [Preprint]

On the quantum origin of potentials. (arXiv:2112.08461v1 [quant-ph])

The dynamics of a quantum particle is governed by its wavefunction, which in turn is determined by the classical potential to which it is subjected. However the wavefunction itself induces a quantum potential, the particle sees’ the sum of the classical and quantum potentials, and there is no way to separate the two. Therefore in principle, part or whole of an observed potential may be attributable to a quantum potential. We examine this possibility and discuss implications.

Axioms for Quantum Gauge Fields. (arXiv:2112.08575v1 [math-ph])

The purpose of this paper is to extend the classical axiom scheme for quantum field theory to include most of the known examples of quantum gauge theories. The axioms are developed in both the Euclidean and Minkowski metrics for space time. We demonstrate that the Euclidean axioms imply the Minkowski (Wightman) axioms. We also prove the reconstruction theorem for Yang-Mills quantum fields as operator-valued tempered distributions with gauge transformation properties.

The universe as a nonlinear quantum simulation. (arXiv:2112.09005v1 [quant-ph])

We investigate a solvable model of nonlinear qubit evolution based on a mapping to an $n$-qubit central spin model in the large $n$ limit, where mean field theory is exact. Extending a theorem of Erd\”os and Schlein to qubits, we establish that the linear central spin model is rigorously dual to a nonlinear qubit. The correspondence explains the origin of qubit torsion, which has been shown by Abrams and Lloyd to enable an exponential speedup for state discrimination in an idealized setting. The duality also suggests that there might not be a sharp distinction between universes evolving according to linear and nonlinear quantum mechanics. In particular, a one-qubit “universe” prepared in a pure state $|\varphi \rangle$ at the time of the big bang and symmetrically coupled to $n$ replicas prepared in the same state, would appear to evolve nonlinearly for any finite time $t>0$ as long as there are exponentially many replicas $n \gg {\rm exp}(O(t))$. Such a universe would appear to support nonlinear quantum evolution.

Four Attitudes Towards Singularities in the Search for a Theory of Quantum Gravity. (arXiv:2112.08531v1 [gr-qc])

Authors: Karen CrowtherSebastian De Haro

Singularities in general relativity and quantum field theory are often taken not only to motivate the search for a more-fundamental theory (quantum gravity, QG), but also to characterise this new theory and shape expectations of what it is to achieve. Here, we first evaluate how particular types of singularities may suggest an incompleteness of current theories. We then classify four different attitudes’ towards singularities in the search for QG, and show, through examples in the physics literature, that these lead to different scenarios for the new theory. Two of the attitudes prompt singularity resolution, but only one suggests the need for a theory of QG. Rather than evaluate the different attitudes, we close with some suggestions of factors that influence the choice between them.

Can quantum mechanics breed negative masses?. (arXiv:2112.08881v1 [gr-qc])

The Casimir effect realizes the existence of static negative energy densities in quantum field theory. We establish physically reasonable conditions for the non-negativity of the total mass of a Casimir apparatus held in equilibrium in the Minkowski background. Specifically, the dynamical equilibrium requires the presence of additional matter to hold the system apart. As long as this extra matter satisfies the dominant energy condition, the mass of the combined system is positive. We discuss the takeaways from the Casimir setting to more general circumstances.

Feyerabend on the quantum theory of measurement: A reassessment

Kuby, Daniel and Fraser, Patrick (2021) Feyerabend on the quantum theory of measurement: A reassessment. [Preprint]

Infinity and Continuum in the Alternative Set Theory

Trlifajová, Kateřina (2021) Infinity and Continuum in the Alternative Set Theory. [Preprint]

A fast push to photon pairs

Nature Physics, Published online: 16 December 2021; doi:10.1038/s41567-021-01410-0

Solid-state sources of entangled photons with tailored properties are key elements for integrated quantum computing. Refractive-index perturbations propagating faster than the speed of light may offer a practical approach for generating entangled photon pairs.

Quantum Entanglement from Classical Trajectories

Author(s): Johan E. Runeson and Jeremy O. Richardson

A long-standing challenge in mixed quantum-classical trajectory simulations is the treatment of entanglement between the classical and quantal degrees of freedom. We present a novel approach that describes the emergence of entangled states entirely in terms of independent and deterministic Ehrenfest…

[Phys. Rev. Lett. 127, 250403] Published Wed Dec 15, 2021

Varieties of Humeanism: an introduction

Comment on Do electromagnetic waves always propagate along null geodesics?’