Observation of two-beam collective scattering phenomena in a Bose-Einstein condensate

TL;DR

This study observes new collective light scattering phenomena in a Bose-Einstein condensate when pumped by two non-interfering beams, revealing regimes of suppressed superradiance and oscillatory dynamics linked to Rayleigh scattering rates.

Contribution

It demonstrates the first experimental observation of two-beam collective scattering effects in a BEC, confirming theoretical predictions of supersolid phases at large scattering rates.

Findings

Two-beam setup suppresses superradiance at low scattering rates.

At high scattering rates, the threshold for scattering is reduced.

Oscillatory quench dynamics observed in the two-beam regime.

Abstract

New phenomena of collective light scattering are observed when an elongated Bose-Einstein condensate is pumped by two non-interfering beams counterpropagating along its long axis. In the limit of small Rayleigh scattering rates, the presence of a second pump beam suppresses superradiance, whereas at large Rayleigh scattering rates it lowers the effective threshold power for collective light scattering. In the latter regime, the quench dynamics of the two-beam system are oscillatory, compared to monotonic in the single-beam case. In addition, the dependence on power, detuning, and atom number is explored. The observed features of the two-beam system qualitatively agree with the recent prediction of a supersolid crystalline phase of light and matter at large Rayleigh scattering rates [S. Ostermann, F. Piazza, and H. Ritsch, Phys. Rev. X 6, 021026 (2016).]