Quantum-enhanced optical phase tracking

TL;DR

This paper demonstrates that using phase-squeezed light in continuous-wave optical phase tracking surpasses the quantum vacuum limit, achieving significantly improved precision by optimizing the degree of squeezing.

Contribution

It introduces a method to surpass the coherent-state limit in optical phase tracking using phase-squeezed states and optimizes squeezing for best performance.

Findings

Achieved 15 ± 4% below the coherent-state limit in phase tracking error.

Optimal squeezing degree depends on the phase variation range.

Method applicable to optical communication and metrology.

Abstract

Tracking a randomly varying optical phase is a key task in metrology, with applications in optical communication. The best precision for optical phase tracking has till now been limited by the quantum vacuum fluctuations of coherent light. Here we surpass this coherent-state limit by using a continuous-wave beam in a phase-squeezed quantum state. Unlike in previous squeezing-enhanced metrology, restricted to phases with very small variation, the best tracking precision (for a fixed light intensity) is achieved for a finite degree of squeezing, due to Heisenberg's uncertainty principle. By optimizing the squeezing we track the phase with a mean square error 15 \pm 4 % below the coherent-state limit.