三维光晶格技术在锶原子光钟中的应用

Due to the large number of atomic samples available for reference, the signal-to-noise of the clock transitions of the optical lattice clocks based on neutral atoms is relatively high and can obtain a higher stability in a relatively short integration time. Now the fractional frequency instability and uncertainty of the best optical clocks based on neutral atoms have achieved the unprecedented level of 10-18, making possible the redefinition of the second of the international system of units (SI) using optical clocks. On the basis of our one-dimensional optical lattice clock of 87Sr, we keep on experimentally investigating three-dimensional (3D) optical lattice in optical clock based on strontium atoms. As the frequency source of the strontium optical clock, it can not only increase the frequency stability of the strontium optical clock by increasing the number and density of the cold atoms in the three-dimensional optical lattice, but also significantly reduce the interaction between the atoms in the lattice and effectively inhibit the collision shift of the atoms. Finally, a simultaneous improvement in the stability and uncertainty of the strontium optical clock, and the advantage of the neutral atomic optical lattice clock, is expected to reduce the uncertainty of the collision shift of the atom below the magnitude of 10-18.

基于中性原子的光晶格钟有大量的原子样品可供参考，因此钟跃迁谱线的信噪比较高，可以在相当短的积分时间内进入更高的稳定度，目前其稳定度和系统不确定度已经进入10-18量级，有可能重新定义国际单位“秒”。本项目在我们现有一维锶原子光晶格钟的基础上,开展三维光晶格技术在锶光钟中的应用研究。作为锶原子光钟的频率源，通过提高三维光晶格中的冷原子数目和密度，不但可以增加锶光钟的频率稳定度，而且可以显著减小晶格格点之间原子的接触相互作用，有效抑制原子的碰撞频移。最终实现锶原子光钟稳定度和不确定度的同步改善，充分发挥中性原子光晶格钟的优势，预期将原子碰撞频移的不确定度减小到10-18量级以下。

光学原子钟的频率稳定度和系统不确定度都已进入E-18量级，较现有基准钟-铯原子喷泉钟高出2个数量级以上，极有可能成为下一代的时间频率基准。为了应对将来国际秒定义变更以及建设我国新一代的时间频率体系，需要研制高性能光学原子钟。碰撞频移是光晶格钟的主要频移项之一，抑制碰撞频移是提高光晶格钟精度的重要技术途径。本项目通过优化提升系统性能，评估了锶原子光晶格钟的自比对频率稳定度，开展了锶原子光钟四项主要频移项的评估，包括碰撞频移、黑体辐射频移、晶格光AC Stark频移、二阶塞曼频移的频移量和系统不确定度的评估。移除钟激光频率漂移导致的自比对测量误差后将光晶格钟自比对稳定度提升至9E-18@E5 s，最终评估的碰撞频移不确定度为7.7E-18，达到了本项目预期的研究效果。自比对频率稳定度和碰撞频移不确定度均进入E-18量级为实现系统不确定度E-18量级的锶原子光晶格钟奠定了良好的实验基础。