Controlling spontaneous-emission noise in measurement-based feedback cooling of a Bose-Einstein Condensate

TL;DR

This paper introduces a novel feedback control method that mitigates measurement-induced heating in Bose-Einstein condensates during continuous optical monitoring, enabling longer measurement times and improved quantum state control.

Contribution

It demonstrates a new feedback control scheme and highlights the importance of multimode quantum-field effects, using the NPW particle filter for accurate simulation of measurement backaction.

Findings

New feedback control reduces heating effects in BEC monitoring.

Measurement backaction is a multimode quantum-field effect.

NPW particle filter effectively simulates continuous measurement dynamics.

Abstract

Off-resonant optical imaging is the most popular method for continuous monitoring of a Bose-Einstein condensate (BEC). However, the disturbance caused by scattered photons places a serious limitation on the lifetime of such continuously-monitored condensates. In this paper, we demonstrate that a new choice of feedback control can overcome the heating effects of the measurement backaction. In particular, we show that the measurement backaction caused by off-resonant optical imaging is a multimode quantum-field effect, as the entire heating process is not seen in single-particle or mean-field models of the system. Correctly simulating such continuously-monitored systems is only possible using the number-phase Wigner (NPW) particle filter, which is a hybrid between the leading techniques for simulating non-equilibrium dynamics in condensates and particle filters for simulating high-dimensional non-Gaussian filters in the field of engineering. The new control scheme will enable long-term continuous measurement and feedback on one of the leading platforms for precision measurement and the simulation of quantum fields, allowing for the possibility of single-shot experiments, adaptive measurements and robust state-preparation and manipulation.