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 171Yb atoms in their spin-1/2 ground states. Correlation between two sequential QNDMs indicates −0.80−0.12+0.11dB 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
@article{arxiv.1301.1016,
title = {Unconditional quantum-noise suppression via measurement-based quantum feedback},
author = {Ryotaro Inoue and Shin-Ichi-Ro Tanaka and Ryo Namiki and Takahiro Sagawa and Yoshiro Takahashi},
journal= {arXiv preprint arXiv:1301.1016},
year = {2013}
}