Unconditional quantum-noise suppression via measurement-based quantum feedback

TL;DR

This paper demonstrates unconditional quantum-noise suppression in a large atomic ensemble using measurement-based feedback, achieving a significant reduction in quantum noise through non-demolition measurements and feedback control.

Contribution

It introduces a method to convert conditional quantum-noise suppression into unconditional suppression in a collective spin system using feedback control based on quantum non-demolition measurements.

Findings

Achieved -0.80 dB quantum noise suppression conditionally.

Demonstrated unconditional noise suppression via feedback control.

Performed shot-noise limited measurements on 3.7×10^5 atoms.

Abstract

We demonstrate unconditional quantum-noise suppression in a collective spin system via feedback control based on quantum non-demolition measurement (QNDM). We perform shot-noise limited collective spin measurements on an ensemble of $3.7\times 10^5$ laser-cooled 171Yb atoms in their spin-1/2 ground states. Correlation between two sequential QNDMs indicates $-0.80^{+0.11}_{-0.12}\,\mathrm{dB}$ quantum noise suppression in a conditional manner. Our feedback control successfully converts the conditional quantum-noise suppression into the unconditional one without significant loss of the noise