Keywords: 
• 低频压缩 /
• 马赫-曾德尔干涉仪 /
• 声频信号测量

Abstract: Measurement of audio signal plays a significant role in many applications,such as gravitational wave detection,bioparticle imaging and magnetometer.In this paper,low-frequency squeezed light is generated by a non-degenerate optical parametric amplifier.In order to avoid the effect of injected light on low-frequency squeezing,an auxiliary laser is used to lock the length of non-degenerate optical parametric amplifier and a method of locking quantum noise is employed to lock the phase between the local light and the squeezed light.By isolating the vibration noises at low-frequency and reducing back action of parasitic interference,the squeezing of (7.1±0.1) dB takes place at 19 kHz.Then the squeezed light is injected into the Mach-Zehnder interferometer to measure an audio signal which drives a piezoelectric transducer to generate a small phase variation between two arms of Mach-Zehnder interferometer.According to the low-frequency squeezing,we realize experimentally the measurement of phase signal at audio frequency which exceeds the shot-noise limit of (3.0±-0.4) dB.The experiment provides technical supports for the generation of low-frequency squeezed light and the measurement of audio signal.Furthermore it can be extended to other quantum measurements,such as high-precision magnetometer and measurement of small-displacement.