Answers are grounded in this paper and cite their sources.
A monolithic doubly resonant optical parametric oscillator produced signal and idler modes at widely separated wavelengths whose amplitude fluctuations were correlated (53.6±{}1.0)% below the vacuum-noise level. The system was used to detect modulated signals well below the shot-noise limit.
No takes yet. Share an insight, caveat, or question.
Nabors et al. (1990) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: