Multimode cavity QED as an active quantum gas microscope*

Optical cavity QED provides a versatile platform with which to explore quantum many-body physics in driven-dissipative systems. Multimode cavities are particularly useful for exploring beyond mean-field physics. The participation of many degenerate cavity modes allows one to have high control over the photon-mediated atom-atom interaction. In a confocal cavity this interaction becomes highly localized. In a related fashion, the tight (super)mode spot also implies an enhanced cavity cooperativity; our measurements imply cooperativities exceeding 25 in the confocal cavity, which enable the observation of phenomena dominated by quantum fluctuations. We experimentally investigate the interaction range of our current confocal cavity setup, demonstrating an asymptotic interaction range of 3 microns, currently limited by mirror aberrations and finite-size effects. A small part of the intracavity field is continuously emitted through the cavity mirrors, providing a direct, spatially resolved observation channel of the atoms within. The photon-mediated interactions enabled by the system, combined with its built-in spatial resolvability, allow it to serve as an active quantum gas microscope.