Rostock 2019 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 52: Quantum Gases (Bosons) V

Q 52.8: Talk

Thursday, March 14, 2019, 15:45–16:00, S HS 037 Informatik

Superradiant phases of a quantum gas in a bad cavity — •Simon B. Jäger¹, John Cooper^2,3, Murray J. Holland^2,3, and Giovanna Morigi¹ — ¹Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany — ²JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA — ³Center for Theory of Quantum Matter, University of Colorado, Boulder, Colorado 80309, USA

We theoretically analyse superradiant emission of light from an ultracold gas of bosonic atoms confined in a bad cavity. The atoms dipolar transition which couples to the cavity is metastable and is incoherently pumped, the atomic motion is affected by the mechanical forces of the cavity standing-wave. By means of a mean-field model we determine the conditions on the cavity parameters and pump rate that lead to steady-state superradiant emission. We show that this occurs when the superradiant decay rate exceeds a threshold determined by the recoil energy, which scales the quantum atom-photon mechanical interactions. When this occurs, superradiant emission is accompanied by the formation of matter-wave gratings that diffract the emitted photons. The stability of these gratings is warranted when the pump rate is larger than a second threshold, below which the emitted light is chaotic. These dynamics are generated by collective quantum interference in a driven-dissipative system. It presents signatures of a peculiar second-order phase transition, where coherent phases of both light and matter emerge and are controlled by entirely incoherent processes.