CONTINUOUS-WAVE QUANTUM-NONDEMOLITION MEASUREMENTS WITH VACUUM AND NONCLASSICAL METER INPUT

QND measurements of the amplitude quadrature of continuous-wave light are performed with a monolithic dual-port degenerate optical parametri c amplifier (OPA). Operated with a vacuum meter input, both output bea ms are squeezed and 33% correlated, demonstrating individually squeeze d twin beams. The sum of the signal and meter transfer coefficients is 1.05, demonstrating operation as a quantum optical tap. The device ex hibits quantum state preparation ability for both signal and meter out put, reaching the conditional variances of -0.8 dB and -2.5 dB, respec tively. An improved quantum measurement is realized by injecting 3.4 d B amplitude-squeezed light into the meter input port of the OPA. This achieves increased correlation and squeezing of the output beams, and both improved operation as a quantum optical tap and as a quantum stat e preparator. The all-solid-state system was operated for up to 5 hour s with high stability.