逼近甚至突破散粒噪声极限的原子钟技术

Atomic clocks play a key role in many important application areas like the Global Navigation Satellite Systems, precision measurement of physical quantities and fundamental constants. Theoretically, the limitation of the frequency stability of atomic clocks is decided by the quantum shot-noise. However, in practice, the performance of atomic clocks is decided by the microwave phase noise and laser noise because these two kinds of noise contribute more deterioration to the frequency stability than quantum shot-noise does. Therefore, reaching the quantum shot-noise limit through eliminating microwave phase noise and laser noise is the key unsettle problem in the atomic clock research filed. In this project, we will further suppress the laser noise by using large frequency detuning orthogonal polarization detection based on magneto-optical rotation effect to improve signal-to-noise ratio of the atomic resonance signal and frequency stability. Meanwhile, we will adopt zero-dead-time technology by interleaving two atomic clocks to constantly measure and regulate the phase of local oscillator and eliminate the Dick effect completely. The zero-dead-time that technology will reduce the sensitivity of the frequency stability of atomic clocks on microwave phase noise. Finally, we will explore the possibility of breakthrough shot-noise limit by detection technique using squeezed vacuum via self-rotation. The frequency stability of atomic clock will reach or even break through the quantum shot-noise limit, and the frequency stability will achieve 5 E - 15 at average time of 10000 seconds with effort of new technologies. The research will provide basis for developing a high performance in-orbit atomic clocks for the next generation of Global Navigation Satellite Systems.

原子钟在卫星导航系统，物理量和基本物理常数精密测量等领域都有重要应用。散粒噪声极限决定了原子钟在理论上可能达到的频率稳定度极限，但是由于微波相位噪声和激光噪声对原子钟频率稳定度的贡献远远大于散粒噪声的贡献，因此如何减小这两项噪声对频率稳定度的影响使原子钟频率稳定度逼近散粒噪声极限是原子钟研究领域长期没有解决的关键科学问题。本项目提出利用大频率失谐的离共振光进行正交偏振探测进一步压缩探测激光噪声；同时利用零死区时间原子钟技术连续测量和补偿本地振荡器的相位完全消除Dick效应，减小原子钟频率稳定度对微波相位噪声的灵敏度，使原子钟的频率稳定度逼近光子散粒噪声极限。最后探索利用偏振自旋转效应产生的真空压缩态光进行原子钟跃迁谱线探测突破散粒噪声极限的可能性。利用这些技术研制万秒频率稳定度力争达到5E-15的POP原子钟样机。期望本项研究结果能为研制下一代卫星导航系统高性能星载原子钟提供技术基础。

课题组在POP原子钟实验平台上围绕压缩探测噪声，提高原子钟跃迁谱线信噪比和压缩谱线宽度，最终优化POP原子钟的闭环频率稳定度的研究目标，开展了零死时间（ZDT）原子钟，Ramsey线宽压缩及短期频率稳定度优化、基于涂石蜡吸收泡的POP原子钟及POP原子钟中长期频率稳定度优化等研究工作，取得了一系列重要研究成果，主要包括：.1..实现了ZDT原子钟技术，完全消除了Dick效应，ZDT-POP原子钟频率稳定度在取样时间为0.01s-1s内近似按照τ-1变化。.2..通常脉冲原子钟Ramsey条纹线宽只能达到1/2T，采用正交偏振探测技术将POP原子钟的Ramsey线宽压缩一半达到1/4T，短期频率稳定度达到1.4×10-13 τ-1/2（1-100s），这一短期频率稳定度已经达到国际上热原子钟的最高水平。.3..开展了基于涂石蜡吸收泡的POP原子钟研究，石蜡泡POP原子钟的短期闭环频率稳定度达到3.9×10-13τ-1/2，这一短期频率稳定度比之前文献报道的石蜡泡原子钟的最好结果提高了一个数量级。.4..开展了POP原子钟中长期频率稳定度优化，万秒频率稳定度达到4.7×10-15。.通过本项目的实施，课题组掌握了逼近散粒噪声极限的微波原子钟技术，完成了POP原子钟原理样机的研制，其万秒频率稳定度达到了4.7E-15，为研制下一代卫星导航系统高性能星载原子钟提供了技术基础。