Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Science. 2012 Sep 21;337(6101):1514-7. doi: 10.1126/science.1225258.
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 until 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 because of Heisenberg's uncertainty principle. By optimizing the squeezing, we track the phase with a mean square error 15 ± 4% below the coherent-state limit.
跟踪随机变化的光相位是计量学中的一项关键任务，在光通信中有广泛的应用。到目前为止，光学相位跟踪的最佳精度一直受到相干光量子真空涨落的限制。在这里，我们通过使用处于相位压缩量子态的连续波光束超越了这个相干态极限。与之前仅限于相位变化非常小的压缩增强计量学不同，由于海森堡不确定性原理，在有限的压缩程度下可以实现最佳的跟踪精度（对于固定的光强）。通过优化压缩，我们以均方误差比相干态极限低 15±4%的水平跟踪相位。
