与锂原子跃迁线相匹配的压缩真空态的实验制备

Squeezed states are a special class of minimum uncertainty states. Even though squeezed states obey the Heisenberg uncertainty principle, its uncertainty of one quadrature is reduced at the expense of the other. Based on the noise feature of the squeezed states, squeezed states can be used for atomic spectrum, electron spin, phase shift and polarization rotation measurement to obtain the measurement precision below the shot noise limit. At present, the shortest wavelength of squeezed vacuum states, generated by down conversion process, is 795 nm. Limited by intracavity loss and thermal effect induced from the BLIIRA (Blue light induced infrared absorption) and linear loss, the generation of the squeezed vacuum states with the shorter wavelength (matching with lithium atom transition line) faces challenges. The project proposes the experimental generation of the 5 dB squeezed vacuum states below the shot noise limit at 671 nm, which is obtained by frequency up-conversion process from squeezed vacuum states at 1550 nm. The wavelength matches with the lithium atom transition line, which can be used for quantum storage and spin measurement. The quantum entanglement between 1550 nm before the frequency up-conversion cavity and 671 nm after the frequency up-conversion cavity can be demonstrated, which open a new way to generate the two-color quantum entanglement with the wavelength band of quantum communication and quantum storage.

压缩光能够在不违反海森堡不确定关系的前提下，通过增加其中一个分量的不确定度，使另一分量的不确定度小于真空态。基于压缩光特殊的噪声特性，可用于原子光谱、电子自旋、相移、偏振面旋转等的测量，获得突破散粒噪声极限的测量精度。目前，利用光学参量下转换过程获得的压缩真空态的最短波长为795 nm，受短波长情况下蓝光导致红外吸收和非线性晶体线性吸收增强而导致的内腔损耗和热效应限制，更短波长（与碱金属原子—锂跃迁线匹配）的压缩真空态的制备面临挑战。本项目拟基于频率上转换技术，利用1550 nm压缩真空态经频率上转换过程制备671 nm的压缩真空态，压缩度低于散粒噪声5 dB以上，该波长与锂原子的跃迁线相匹配，可用于基于锂原子的量子态存储、电子自旋测量等；频率上转换腔前的1550 nm压缩光与频率上转换后的671 nm压缩光是一对纠缠光，为制备量子通信和量子存储波段的双色连续变量量子纠缠态提供了新的方案。

压缩光能够在不违反海森堡不确定关系的前提下，通过增加其中一个分量的不确定度，使另一分量的不确定度小于真空态。基于压缩光特殊的噪声特性，可用于原子光谱、电子自旋、相移、偏振面旋转等的测量，获得突破散粒噪声极限的测量精度。目前，利用光学参量下转换过程获得的压缩真空态的最短波长为795 nm，受短波长情况下蓝光导致红外吸收和非线性晶体线性吸收增强而导致的内腔损耗和热效应限制，更短波长（与碱金属原子—锂跃迁线匹配）的压缩真空态的制备面临挑战。本项目详细分析了高压缩度、高稳定性压缩态光场制备中的主要限制因素：光学损耗与位相抖动，为高质量非经典光场的制备解决了关键原理和技术问题。利用系列关键技术实验制备了波长为1064nm的压缩真空态，压缩度为13.8 dB；制备了波长为1550nm的压缩真空态，压缩度为12.3 dB，同时完成了11.1dB的纠缠态光场的输出；制备了波长为532 nm的明亮压缩态光场，压缩度为2.1dB；在实验上同时制备出四对边带纠缠态其纠缠度均高于10.0 dB。该结果将为量子信息的发展提供优质的非经典光场，为精密测量领域提供了重要的量子增强技术手段。