Squeezing-enhanced fiber Mach-Zehnder interferometer for low-frequency phase measurement

Abstract

We propose and experimentally demonstrate a quantum-enhanced fiber Mach-Zehnder interferometer for low-frequency phase measurement beyond the shot-noise limit using a high-frequency squeezing technique. The local oscillator field is amplitude-modulated in the MHz range and is then demodulated to avoid the technical noise that occurs at low frequencies. After measurement of the phase noise at a frequency of tens of kHz, an improvement of ∼2 dB relative to the shot-noise level is achieved. Additionally, the amplitude modulation depth has no significant effect on the phase noise improvement of the interferometer when deployed in our experimental configuration. The current scheme introduces a quantum technique into the fiber-based measurements, particularly for the low frequency range, and this scheme has potential applications in the high-precision fiber sensing of temperature, strain, and various other parameters.