Observation of entanglement in a cold atom analog of cosmological preheating

TL;DR

This study demonstrates entanglement between collective excitations in a Bose-Einstein condensate, serving as an analog model for cosmological preheating, and highlights the quantum origins of particle production in the early universe.

Contribution

It provides the first experimental observation of entanglement in a cold atom analog of cosmological preheating, linking quantum fluctuations to early universe phenomena.

Findings

Entanglement observed between quasiparticle pairs with opposite momenta.

Vacuum fluctuations seed parametric growth of excitations.

Non-classical correlations diminish as the system evolves.

Abstract

We observe entanglement between collective excitations of a Bose-Einstein condensate in a configuration analogous to particle production during the preheating phase of the early universe. In our setup, the oscillation of the inflaton field is mimicked by the transverse breathing mode of a cigar-shaped condensate, which parametrically excites longitudinal quasiparticles with opposite momenta. After a short modulation period, we observe entanglement of these pairs which reveals the role played by vacuum fluctuations in seeding the parametric growth, confirming the quantum origin of the excitations. As the system continues to evolve, we observe a decrease in correlations and a disappearance of non-classical features. These point towards future experimental probes of the late-time nonlinear regime where further analogies can be drawn with reheating, i.e. the thermalization of the post-inflationary Universe.