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边带场之间的纠缠来揭示。在许多原理证明实验中，特别是光的压缩真空态已被用于减少量子计量中的光子计数噪声（散粒噪声）。虽然非线性晶体中的参量下转换可以有效地产生近红外波长的压缩光，但这种方法无法有效地产生可见光甚至紫外波长的压缩光。然而，在计量学中，更短的波长是可取的，因为它们提供更高的相位信号，并且对于给定的光功率，也提供更高的信噪比。在本项目中，将首次通过频率上转换1550nm的压缩场，在532nm处产生光的压缩真空态。该光将用于演示532nm的台式激光干涉仪，其灵敏度优于短噪声限制。对该干涉仪的定量分析表明，该干涉仪的绝对位移灵敏度优于在相同的激光功率和相同的压缩系数下工作的相同干涉仪的灵敏度，但波长更大。这个项目的结果也将在量子信息科学中有应用，因为非经典光的频率上变频可以提供通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.