Abstract
We present an active feedback scheme acting continuously on the state of a quantum gas dispersively coupled to a high-finesse optical cavity. The quantum gas is subject to a transverse pump laser field inducing a self-organization phase transition, where the gas acquires a density modulation and photons are scattered into the resonator. Photons leaking from the cavity allow for a real-time and non-destructive readout of the system. We stabilize the mean intra-cavity photon number through a micro-processor controlled feedback architecture acting on the intensity of the transverse pump field. The feedback scheme can keep the mean intra-cavity photon number nph constant, in a range between nph = 0.17(4) and nph = 27.6(5), and for up to 4 s. Thus we can engage the stabilization in a regime where the system is very close to criticality as well as deep in the self-organized phase. The presented scheme allows us to approach the self-organization phase transition in a highly controlled manner and is a first step on the path towards the realization of many-body phases driven by tailored feedback mechanisms.
Highlights
Ultracold atomic quantum gases are a well-suited platform to study transitions and crossovers between different phases of matter
By tuning the strength of an external drive field, the combined atom-cavity system is undergoing a self-organization phase transition which can be mapped onto the Dicke model, which is of fundamental importance in quantum optics [12,13,14,15] and has been recently experimentally realized in cold atoms [7]
We developed a microprocessor-based active feedback scheme which stabilizes the number of mean intra-cavity photons during self-organization of a Bose–Einstein condensate (BEC) in an optical cavity
Summary
Katrin Kroeger , Nishant Dogra1,2 , Rodrigo Rosa-Medina , Marcin Paluch, Francesco Ferri , Tobias Donner and Tilman Esslinger.
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