Enhanced feedback-cooling of a Bose-Einstein condensate via stroboscopic adaptive measurement*

Feedback cooling based on real-time quantum measurements could be used to create Bose-Einstein condensates (BECs) with larger atom numbers compared with traditional evaporative cooling. Previous theoretical works have shown that for an almost pure condensate, heating caused by a continuous dispersive optical measurement can be overcome via feedback to the BEC’s confining trapping potentials, enabling cooling close to the ground state [Phys. Rev. A 82, 043632, 2010]. Here we extend this model and improve upon this feedback protocol by (1) considering a stroboscopic measurement scheme and (2) adaptively choosing measurement parameters, with the aim of decreasing measurement backaction (compared with the continuous, fixed measurement case) whilst still obtaining the information needed for efficient real-time feedback cooling. We will present the details of the adaptive, stroboscopic measurement-based feedback control and show it delivers improved cooling performance over a continuous measurement protocol with fixed parameters. Our results demonstrate the importance of optimizing the information-backaction trade-off for efficient feedback control, both within the particular context of feedback cooling a BEC and for quantum systems more generally.