Many-body physics in two-component Bose-Einstein condensates in a cavity: fragmented superradiance and polarization

TL;DR

This paper explores how laser-pumped two-component Bose-Einstein condensates in a cavity exhibit complex many-body phenomena, including self-organization, fragmentation, and breakdown of the Dicke model at high pump powers.

Contribution

It introduces a detailed analysis of the ground state and phase transitions in a two-component BEC within a cavity, revealing fragmented superradiance and limitations of the Dicke model.

Findings

Identification of self-organization thresholds

Observation of BEC fragmentation at high pump power

Breakdown of Dicke model applicability in the fragmented phase

Abstract

We consider laser-pumped one-dimensional two-component bosons in a parabolic trap embedded in a high-finesse optical cavity. Above a threshold pump power, the photons that populate the cavity modify the effective atom trap and mediate a coupling between the two components of the Bose-Einstein condensate. We calculate the ground state of the laser-pumped system and find different stages of self-organization depending on the power of the laser. The modified potential and the laser-mediated coupling between the atomic components give rise to rich many-body physics: an increase of the pump power triggers a self-organization of the atoms while an even larger pump power causes correlations between the self-organized atoms -- the BEC becomes fragmented and the reduced density matrix acquires multiple macroscopic eigenvalues. In this fragmented superradiant state, the atoms can no longer be described as two-level systems and the mapping of the system to the Dicke model breaks down.