Approaching quantum-limited phase tracking with a large photon flux in a fiber Mach-Zehnder interferometer

The real-time phase tracking has a large number of applications in the precise measurement of various physical parameters. The classical limit of fiber phase tracking has been realized with homodyne detection under a low photon flux (typically similar to 10(6) s(-1)). However, it is still difficult to approach the coherent state limit when measuring a weak phase fluctuation in real time by using a larger photon flux. In this work, we propose a fiber Mach-Zehnder system and experimentally demonstrate a nearly quantum-limited phase tracking with mean photon numbers of similar to 3.7x10(10) s(-1). In the experiment, the input state is a continuous-mode coherent state and an adaptive Kalman filter is used to construct a phase-locked loop. We effectively track a very weak random phase varying between - 0.07 and + 0.07 radians, and the minimum mean-squared error is optimized to 2.5x10(-5) which approaches the coherent state limit. Our method has potentially applications for fiber-based real-time sensing and measurements.

Automated summary

In this study, a fiber Mach-Zehnder system is proposed to achieve nearly quantum-limited phase tracking, demonstrating potential applications in fiber-based real-time sensing and measurements.