Sign-changing photon-mediated atom interactions in multimode cavity QED

TL;DR

This paper demonstrates a novel sign-changing, nonlocal photon-mediated interaction between Bose-Einstein condensates in a multimode cavity, revealing new symmetry-breaking phenomena and potential for quantum simulation of complex systems.

Contribution

It introduces a unique nonlocal interaction mediated by Gouy phase shifts in a multimode cavity, enabling exploration of frustrated many-body systems and quantum neural networks.

Findings

Observation of sign-changing, nonlocal atom interactions.

Detection of Z_2-symmetry-breaking in atomic density patterns.

Identification of a nonequilibrium Dicke-type phase transition.

Abstract

Sign-changing interactions constitute a crucial ingredient in the creation of frustrated many-body systems such as spin glasses. We present here the demonstration of a photon-mediated sign-changing interaction between Bose-Einstein condensed (BEC) atoms in a confocal cavity. The interaction between two atoms is of an unusual, nonlocal form proportional to the cosine of the inner product of the atoms' position vectors. This interaction arises from the differing Gouy phase shifts of the cavity's degenerate modes. Moreover, these Gouy phase anomalies induce an extra pattern of Z_2-symmetry-breaking in the atomic density-wave self-ordering that arises from a nonequilibrium Dicke-type phase transition in the system. This state is detected via the holographic imaging of the cavity's superradiant emission. Together with Ref. [1], we explore this interaction's influence on superradiant phase transitions in multimode cavities. Employing this interaction in cavity QED spin systems may enable the creation of artificial spin glasses and quantum neural networks.