We experimentally demonstrate quantum behavior of a macroscopic atomic spin oscillator in the acoustic frequency range. Quantum back-action of the spin measurement, ponderomotive squeezing of light, and oscillator spring softening are observed at spin oscillation frequencies down to 6 kHz. Quantum noise sources characteristic of spin oscillators operating in the near-DC frequency range are identified and means for their mitigation are presented. These results constitute an important step towards quantum noise reduction and entanglement-enhanced sensing in the acoustic range using a negative-mass reference frame. In particular, the results are relevant for broadband noise reduction in gravitational wave detectors.
@article{arxiv.2303.11029,
title = {Acoustic frequency atomic spin oscillator in the quantum regime},
author = {Jun Jia and Valeriy Novikov and Tulio Brito Brasil and Emil Zeuthen and Jörg Helge Müller and Eugene S. Polzik},
journal= {arXiv preprint arXiv:2303.11029},
year = {2024}
}