Hannover 2020 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 22: Posters: Quantum Optics and Photonics II

Q 22.66: Poster

Tuesday, March 10, 2020, 16:30–18:30, Empore Lichthof

Continuous feedback and spin-changing processes in a quantum gas coupled to a cavity — •Francesco Ferri, Fabian Finger, Katrin Kroeger, Rodrigo Rosa-Medina, Nishant Dogra, Marcin Paluch, Tobias Donner, and Tilman Esslinger — Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland

We realize a driven-dissipative version of the Dicke model by coupling a Bose-Einstein condensate (BEC) to an optical cavity, and illuminating it with a transverse pump laser. Above a critical pump strength, the system undergoes a phase transition to a superradiant phase exhibiting self-ordering of the atomic density. The system’s state can be accessed non-destructively by detecting the photons leaking from the cavity.

Here, we report on two recent advances in this context. First, we describe the implementation of an active feedback scheme to stabilize the mean intra-cavity photon number in the superradiant phase, by acting back on the pump strength. Feedback allows to approach the phase transition with a high degree of control and to extend the lifetime of the system close to criticality. Our results are a first step towards more complex feedback schemes leading to exotic many-body phases, such as limit cycles or Floquet time crystals.

In a second set of experiments, a double-frequency pump laser induces cavity-assisted Raman transitions between different spin and motional states of the BEC. An extended, fully tunable Dicke model is realized, where competing coherent and incoherent spin-changing processes occur. This scheme opens new avenues for investigating long-range spin interactions and novel magnetic phases.