基于零拍探测和压缩真空光输入增强Sagnac效应

利用量子技术增强Sagnac效应提高陀螺输出精度具有重要的研究意义, 是实现全自主导航的重要途径. 以相干态激光作为输入光源的光学陀螺因真空零点波动使其输出精度限制于散粒噪声极限而难以提高. 为减小真空波动的影响, 提出在激光输入的分束器的另一输入端输入压缩真空光并结合平衡零拍探测技术的方法增强Sagnac效应. 理论分析表明Sagnac效应性能得到有效提升: 干涉输出的灵敏度检测极限和动态范围均随着压缩程度的增加而呈指数级增长. 该方法只需对经典光学陀螺做少量改动就可实现, 是提高光学陀螺输出精度的一种新方法.

A scheme for Sagnac effect improvement with squeezed vacuum input and homodyne detection

There has been much interest in improving gyroscope precision with quantum technology for realizing autonomous navigation. The laser light in coherent state cannot reach higher precision under shot-noise limit (SNL) caused by vacuum zero energy fluctuation, which restricts the further improvement of optical gyroscope precision. Quantum mechanics reckons that one unused port of the beam splitter (BS) is inputted with vacuum, which results in vacuum fluctuation, while another port is inputted with the laser light in optical gyroscope. In order to compress the vacuum fluctuation, we design an experimental scheme, in which squeezed vacuum light is used as another incident light into the unused port of Sagac interferometer in optical gyroscope. We analyze the physical process of this scheme theoretically and develop the quantum balanced homodyne detection technique to retrieve the relative phase information of Sagac interferometer output. There are two most important conditions that we should pay attention to. 1) We should ensure that the phase of local oscillator light arg(α _L), the phase of coherent light arg (α_c) and the angle of squeezed direction arg(μν) in the squeezed vacuum light satisfy the condition, i.e., arg (α _L²)-arg (μν) = πup and arg (α _L)-arg (α_c) = 0 when we perform quantum balanced homodyne detection technique for the best sensitivity δφ = e^-Gδφ_SNL, where G denotes the squeezed degree; 2) only by deriving the fields from one common source can we ensure coherence among the squeezed vacuum, probe and local oscillator. Although the requirements for experimental settings are strict, we can meet the requirement with careful calibration. Numerical analysis shows that this proposed scheme provides much higher precision below SNL: both sensitivity detection limit and dynamic range grow with an exponential rate as the squeezed degree grows. The current technology for squeezed vacuum generation by using two consecutive crystals with the optic axes tilted allows us to reach a value as high as G ≈ 16 of squeezed degree. Only by inputting such squeezed vacuum light into the unused port of BS in the optical gyroscope, can we attain sensitivity detection limit and dynamic range with increment by 10⁸. Our approach is a new scheme for improving optical gyroscope with current available technology.