Fermion production at the boundary of an expanding universe: a cold-atom gravitational analogue

TL;DR

This paper investigates fermion production in an expanding universe using a (1+1)-dimensional model with boundary effects, proposing a cold-atom quantum simulation approach to explore topological phenomena and particle creation.

Contribution

It introduces lattice regularizations for simulating fermion production in curved spacetime and demonstrates how boundary zero modes can be populated, linking topological states with cosmological particle creation.

Findings

Wilson-type discretization reveals boundary zero modes linked to particle production.

Particle production can populate boundary zero modes, unlike naive discretizations.

Proposes a cold-atom quantum simulation scheme with real-time control and band-mapping measurements.

Abstract

We study the phenomenon of cosmological particle production of Dirac fermions in a Friedman-Robertson-Walker spacetime, focusing on a (1+1)-dimensional case in which the evolution of the scale factor is set by the equations of Jackiw-Teitelboim gravity. As a first step towards a quantum simulation of this phenomenon, we consider two possible lattice regularizations, which allow us to explore the interplay of particle production and topological phenomena in spacetimes with a boundary. In particular, for a Wilson-type discretization of the Dirac field, the asymptotic Minkowski vacua connected by the intermediate expansion corresponds to symmetry-protected topological groundstates, and have a boundary manifestation in the form of zero-modes exponentially localized to the spatial boundaries. We show that particle production can also populate these zero modes, which contrasts with the situation with a na\"ive-fermion discretization, in which conformal zero-mass fields exhibit no particle production. We present a scheme for the quantum simulation of this gravitational analogue by means of ultra-cold atoms in Raman optical lattices, which requires real-time control of the Raman-beam detuning according to the scale factor of the simulated spacetime, as well as band-mapping measurements.