自由空间远程时间传递的量子优化技术研究

High-precision time synchronization plays an important role in the areas of fundamental research and applications. Accompanying with the remarkable improvements in the ability of generating and measuring high-accuracy time-frequency signal, seeking for new time-transfer techniques between distant clocks with much further improved accuracy attracts attensions world-widely. The time-transfer technique based on optical pulses has the highest-precision presently, the further improvement in the accuracy is heavily dependent on the time-domain properties of the pulse as well as the sensitivity of the applied measurement on the exchanged pulse. Recent investigations shows that, utilizing quantum techniques, i.e. quantum measurement technique and quantum optical pulse source, can lead to a new limit on the measured timing information. Furthermore, it can be immune from atmospheric parameters, such as pressure, temperature, humidity and so on. The quantum measurement technique refers to the homodyne detection combined with an appropriately pulse-shaped mode-locked femtosecond laser as the local oscillator. The quantum optical pulse source refers to a multimode squeezed mode-locked femtosecond laser along the certain orthogonal quadratures. Such quantum improvements on time-transfer have a bright prospect in the future applications requiring extremely high-accuracy timing and ranging. .This project will investigate on key techniques in the quantum improved time-transfer technology. The main contents are focused on two parts. The first part is about the investigation of the optimal time-domain pulse differentiation of the local referenced femtosecond laser. The second part is about the generation and optimization of the squeezing in the quantum femtosecond comb. The achievements will form a technical basis for the future realization of sub-femtosecond time transfer system.

随着时间频率的研究水平不断提高，实现比现有精度大幅提高的新一代时间传递技术的研究受到广泛关注。激光脉冲时间传递作为目前自由空间时间传递精度最高的技术，其精度提高与采用的探测手段和脉冲光量子特性紧密关联。利用平衡零拍探测技术结合脉冲整形的本地参考源，可实现实时且精度达到散粒噪声极限的时间延迟测量，测量准确度还可免受自由空间温度、压强、湿度等参数变化导致的群延迟变化影响；应用具有压缩特性的量子光频梳替代传统光频梳，将使时间延迟的测量精度突破散粒噪声极限。因此，基于量子测量和量子光源的量子优化在提高自由空间远程时间传递精度方面具有巨大应用潜力，是未来时间频率的高精度传输与比对技术的重要研究方向。本项目拟开展自由空间远程光学时间传递精度量子优化的关键技术研究：主要围绕本地参考脉冲时域整形，量子压缩光脉冲源的产生开展理论和实验研究，为后续开展亚飞秒量级的超高精度时间传递提供技术基础。

随着时间频率的研究水平不断提高，实现比现有精度大幅提高的新一代时间传递技术的研究受到广泛关注。激光脉冲时间传递作为目前自由空间时间传递精度最高的技术，其精度提高与采用的探测手段和脉冲光量子特性紧密关联。利用平衡零拍探测技术结合脉冲整形的本地参考源，可实现实时且精度达到散粒噪声极限的时间延迟测量，测量准确度还可免受自由空间温度、压强、湿度等参数变化导致的群延迟变化影响；应用具有压缩特性的量子光频梳替代传统光频梳，将使时间延迟的测量精度突破散粒噪声极限。因此，基于量子测量和量子光源的量子优化在提高自由空间远程时间传递精度方面具有巨大应用潜力，是未来时间频率的高精度传输与比对技术的重要研究方向。本项目开展了自由空间远程光学时间传递精度量子优化的关键技术研究：主要围绕用于平衡零拍探测的本地参考脉冲时域整形，量子压缩光脉冲源的产生开展理论和实验研究。经过三年的项目实施，本项目的研究内容和目标均顺利完成。主要成果包括：（1）完成了脉冲一阶与二阶包络的时间微分整形，其中一阶电场保真度为98.37%，能量转换效率为11.10%，二阶电场保真度为97.32%，能量转换效率为3.53%。另外还实现了脉冲电场的一阶微分整形，其电场保真度为99.53%，能量转换效率为72.12%。（2）完成了量子光频梳的实验装置搭建，系统稳定性良好；在注入45mW泵浦光条件下，信号场的经典增益达到40倍；在分析频率1MHz下测量到2.5dB压缩，根据系统总探测效率0.599，扣除损耗后得到该量子光频梳光场的压缩度为5.7dB。（3）由于高灵敏时延测量精度主要受限于飞秒脉冲激光的载波包络相位噪声，研究并实现了利用共振无源腔抑制飞秒脉冲的激光强度、相位噪声，使其在探测频率2MHz以下达到散粒噪声极限。本项目的实施为后续开展亚飞秒量级的超高精度时间传递提供了有力的技术支撑。