Loss-Tolerant Detection of Squeezed States in the 2 μ m Region
K. M. Kwan, T. McRae, Jiayi Qin, Daniel W. Gould, S. Chua, J. Junker, R. Iden, V. B. Adya, M. J. Yap, Bram J. J. Slagmolen, David E. McClelland, Robert L. Ward · Physical Review Letters · 2026
Squeezed states of light enable quantum-enhanced measurements but are limited by optical loss, particularly at 2 μm where photodiode efficiency is low. We report the first loss-tolerant, audio-band squeezed light detection at 1984 nm by using a phase-sensitive amplifier to amplify the squeezed vacuum prior to detection. This technique increases the effective detection efficiency from 74% to 95% and increases the observed squeezing from 4 to 8 dB, the highest level of squeezing observation reported at this wavelength. Additionally, the vacuum to dark-noise clearance increases, extending the effective measurement bandwidth toward lower frequencies. This approach is largely wavelength independent, extending high-fidelity quantum measurements to future gravitational-wave detectors and related quantum technologies.