Frequency upconversion of squeezed vacuum states of light

光的压缩态是量子物理学的核心，这一事实可以通过它们的边带场之间的纠缠来揭示。在许多原理验证实验中，特别是光的压缩真空态已被用于减少量子计量学中的光子计数噪声（散粒噪声）。然而，在近红外波长处的压缩光可以通过非线性晶体中的参数下变频有效地产生，这种方法不能有效地产生在可见光或甚至在UV波长处的压缩光。然而，较短的波长在计量学中是期望的，因为它们提供较高的相位信号，并且对于给定的光功率还提供较高的信噪比。在这个项目中，将首次通过对1550nm的压缩光场进行频率上转换来产生532nm的压缩真空态光。该光将用于演示532 nm处的台式激光干涉仪，其灵敏度优于散粒噪声极限。对干涉仪的定量分析将证明，绝对位移灵敏度优于在相同的激光功率和相同的压缩因子下操作的相同干涉仪的灵敏度，但是在更大的波长下。该项目的结果也将在量子信息科学中得到应用，因为非经典光的频率上转换可以提供电信波长和量子存储设备之间的接口。

Squeezed states of light are at the very heart of quantum physics, a fact which is e.g. revealed by the presents of entanglement between their sideband fields. In many proof-of-principle experiments in particular squeezed vacuum states of light have been used to reduce the photon counting noise (shot-noise) in quantum metrology. Whereas squeezed light at near infra-red wavelengths can efficiently be generated by parametric downconversion in nonlinear crystals, this approach fails for efficient squeezed light generation at visible or even at UV wavelengths. Shorter wavelengths, however, are desirable in metrology, because they provide a higher phase signal and also a higher signal-to-shot-noise-ratio for a given light power. In this project squeezed vacuum states of light will be generated at 532nm by frequency upconverting a squeezed field at 1550nm for the first time. The light will be used to demonstrate a table-top laser interferometer at 532nm with a sensitivity better than the shot-noise limit. A quantitative analysis of the interferometer will prove that the absolute displacement sensitivity is better than the sensitivity of an identical interferometer operated with the same laser power and the same squeezing factor, but at a larger wavelength. The results of this project will also have applications in quantum information science since the frequency upconversion of nonclassical light may provide the interface between telecommunication wavelengths and quantum storage devices.