Feedback cooling Bose gases to quantum degeneracy

TL;DR

This paper introduces a novel feedback cooling method for Bose gases that achieves quantum degeneracy with significantly less atomic loss than traditional evaporative cooling, enabling enhanced quantum applications.

Contribution

The authors demonstrate a new feedback cooling technique for Bose gases that overcomes limitations of evaporative cooling, with robustness to experimental imperfections.

Findings

Feedback cooling can produce high-purity Bose-Einstein condensates.

The method reduces atomic loss compared to evaporative cooling.

Robustness to detection imperfections and control delays was confirmed.

Abstract

Degenerate quantum gases are instrumental in advancing many-body quantum physics and underpin emerging precision sensing technologies. All state-of-the-art experiments use evaporative cooling to achieve the ultracold temperatures needed for quantum degeneracy, yet evaporative cooling is extremely lossy: more than 99.9% of the gas is discarded. Such final particle number limitations constrain imaging resolution, gas lifetime, and applications leveraging macroscopic quantum coherence. Here we show that atomic Bose gases can be cooled to quantum degeneracy using real-time feedback, an entirely new method that does not suffer the same limitations as evaporative cooling. Through novel quantum-field simulations and scaling arguments, we demonstrate that an initial low-condensate-fraction thermal Bose gas can be cooled to a high-purity Bose-Einstein condensate (BEC) by feedback control, with substantially lower atomic loss than evaporative cooling. Advantages of feedback cooling are found to be robust to imperfect detection, finite resolution of the control and measurement, time delay in the control loop, and spontaneous emission. Using feedback cooling to create degenerate sources with high coherence and low entropy enables new capabilities in precision measurement, atomtronics, and few- and many-body quantum physics.