Abstract
Optical cavity QED provides a platform with which to explore quantum many-body physics in driven-dissipative systems. Single-mode cavities provide strong, infinite-range photon-mediated interactions among intracavity atoms. However, these global all-to-all couplings are limiting from the perspective of exploring quantum many-body physics beyond the mean-field approximation. The present work demonstrates that local couplings can be created using multimode cavity QED. This is established through measurements of the threshold of a superradiant, self-organization phase transition versus atomic position. Specifically, we experimentally show that the interference of near-degenerate cavity modes leads to both a strong and tunable-range interaction between Bose-Einstein condensates (BECs) trapped within the cavity. We exploit the symmetry of a confocal cavity to measure the interaction between real BECs and their virtual images without unwanted contributions arising from the merger of real BECs. Atom-atom coupling may be tuned from short range to long range. This capability paves the way toward future explorations of exotic, strongly correlated systems such as quantum liquid crystals and driven-dissipative spin glasses.
Highlights
Cavity QED provides strong light-matter coupling [1]
We exploit the symmetry of a confocal cavity to measure the interaction between real Bose-Einstein condensates (BECs) and their virtual images without unwanted contributions arising from the merger of real BECs
The driven-dissipative, openquantum-system nature of cavity QED can change the character of quantum phase transitions, providing a new window into quantum nonequilibrium physics [10,11]
Summary
Cavity QED provides strong light-matter coupling [1]. For example, exotic nonlinear optical properties arise in cavity systems with atom-mediated photon-photon interactions [2]. [32] observed supermodes in a thermal-gas multimode cavity QED system, where a supermode is the mixture of bare cavity modes by the atomic dielectric, in a configuration where the cavity modes were close to resonance with bare atomic transitions This contrasts with the single-mode experiments mentioned above, where the bare cavity modes are nonresonant, and the superradiant state arises from a two-photon transition involving an external transverse pump. With this transversely pumped, far-detuned configuration, condensation of supermode-density-wave polaritons was subsequently demonstrated in Ref. The Appendix discusses in greater detail the theoretical calculation of the photon-mediated atom-atom interaction
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