We report quantum enhancement of Faraday rotation spin noise spectroscopy by polarization squeezing of the probe beam. Using natural abundance Rb in 100 Torr of N_2 buffer gas, and squeezed light from a sub-threshold optical parametric oscillator stabilized 20 GHz to the blue of the D_1 resonance, we observe that an input squeezing of 3.0 dB improves the signal-to-noise ratio by 1.5 dB to 2.6 dB over the combined (power)⊗(number density) ranges (0.5 mW to 4.0 mW )⊗(1.5 x 10^{12} cm^{-3} to 1.3 x 10^{13} cm^{-3}), covering the ranges used in optimized spin noise spectroscopy experiments. We also show that squeezing improves the trade-off between statistical sensitivity and broadening effects, a previously unobserved quantum advantage.
@article{arxiv.1509.05653,
title = {Squeezed-light spin noise spectroscopy},
author = {Vito Giovanni Lucivero and Ricardo Jiménez-Martínez and Jia Kong and Morgan W. Mitchell},
journal= {arXiv preprint arXiv:1509.05653},
year = {2016}
}