Unconditional quantum-noise suppression via measurement-based quantum feedback
Ryotaro Inoue, Shin-Ichi-Ro Tanaka, Ryo Namiki, Takahiro Sagawa, and Yoshiro Takahashi
Accepted
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 3.7×105 laser-cooled 171\textYb atoms in their spin-1/2 ground states. Correlation between two sequential QNDMs indicates -0.80+0.11-0.12 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 reduction level.