Hong Chang

空间锶原子光晶格钟由地面调试转入在轨微重力环境后，基于¹S₀-³P₁跃迁的窄线宽冷却的俘获力和重力之间的平衡状态产生改变，在本文实验参数下窄线宽冷却原子团的平衡位置发生约为0.595 mm偏移，进而诱发光晶格束腰与窄线宽冷却原子团之间的空间失配．本文基于689 nm窄线宽冷却原子团在重力场和磁场共同作用下的动力学原理，提出利用外加均匀补偿磁场平移磁光阱磁场零点的主动位置补偿理论方案．以空间光钟镜像件物理真空腔体作为实验平台，开展了重力方向翻转的窄线宽原子冷却实验研究．磁光阱磁场梯度约为10 Gs/cm的条件下，在z轴增加122.762 µT的线性均匀补偿磁场，可将翻转状态下的窄线宽冷却原子团重新移回晶格光束腰位置，光晶格原子数恢复至翻转前的水平．实验上测量了不同补偿磁场强度下的光晶格强度，结果表明，对于空间光钟系统，补偿磁场的有效带宽为96.976(2438)µT．本研究不仅证实了基于磁场零点平移法的窄线宽冷却原子位置调控方法的可行性，而且为空间锶原子光钟在微重力条件下实现高效光晶格装载提供数据支撑．

We present a measurement of the absolute frequency of the | 5 s 2 1 S 0 ⟩ → | 5 s 5 p 3 P 0 ⟩ transition in the SrII optical lattice clock at National Time Service Center, performed using a frequency link to International Atomic Time to provide traceability to the International System of Units second. Spanning one-year period with a total oprational duration of approximately 2700 hours, the measurement yields an absolute frequency to be 429 228 004 229 872.95(7) Hz, corresponding to a relative frequency uncertainty of 1.6 × 10 − 16 . This result is in good agreement with the 2025 Bureau of Weights and Measures recommended frequency and is anticipated to contribute to the future update of the CIPM recommendation frequency of the secondary frequency standards.

The microgravity environment modifies the resonance condition that is formed with the participation of gravity in the 689 nm narrow-line magneto-optical trap (red MOT) of a ground-based strontium optical clock. Consequently, a cooling scheme optimized under standard 1g ground-commissioning conditions cannot be directly transferred to an in-orbit space optical clock. In this work, we establish a one-dimensional semiclassical Monte Carlo stochastic dynamics model along the ground-gravity direction to study the cooling dynamics, spatial distribution, and position compensation of a 88Sr narrow-line MOT under microgravity. The simulations show that directly applying ground-optimized parameters in microgravity leads to heating, cloud broadening, and displacement from the lattice position calibrated on the ground. Reducing the detuning can produce a smaller spatial distribution, but this behavior is mainly phase-space truncation and cannot maintain a sufficient effective atom number. We propose a dynamic-control scheme in which the laser detuning and intensity are continuously ramped, achieving an atomic temperature below 3 μK under microgravity while retaining more than 98% of the atoms in the MOT, outperforming the 1g ground-gravity reference case. On this basis, magnetic-gradient screening is used to obtain a cloud size matched to the optical-lattice mode. After an additional compensation magnetic field is introduced, the deviation between the narrow-line MOT center and the lattice position is ∼2.4 μm, far smaller than the transverse scale of the lattice beam. These results provide a physical picture and theoretical guidance for in-orbit commissioning of the narrow-line MOT in a strontium optical clock on the Chinese Space Station.

The 1626 nm laser is an essential component for conducting superlattice research on the strontium atomic clock platform. The superlattice constructed with the 1626 nm and 813 nm lasers will facilitate cutting-edge quantum information research focused on topological quantum states transport. We demonstrate an idler-resonant optical parametric oscillator that achieves 1626 nm laser output based on pump enhancement technology. Through a well-designed external cavity, a laser output of 127 mW at 1626 nm has been achieved, with a corresponding pump quantum conversion efficiency of 50% and a pump threshold of 110 mW. The long-term power stability of the output laser is ±1.5% per hour. Variations in the pump cavity modes under different experimental conditions have been measured, and the impedance matching process of the pump light within the cavity has been discussed. The 1626 nm laser and the associated technologies reported in this manuscript will provide optical support for the investigation of superlattice physics on the strontium optical lattice clock platform.

Owing to their exceptional performance characteristics, optical atomic clocks enable the generation of time scales that demonstrate superior accuracy and stability compared to conventional microwave clocks. This paper presents an experimental optical time scale based on the NTSC-SrⅡ optical lattice clock as the reference and a hydrogen maser as the flywheel oscillator. The time scale TS (SrⅡ), generated through post-processing analysis over a two-month period, achieves a peak-to-peak time variation of 0.39 ns relative to Coordinated Universal Time (UTC) and reaches a frequency stability of 1.94 × 10 ⁻¹⁶ at 5 d. In addition, a physical optical time scale TS*(SrⅡ) was realized for approximately one month, and the peak-to-peak time difference is 0.3 ns compared to UTC. These results demonstrate that optical time scales maintain competitive performance even when the optical clock operates with limited and non-uniformly distributed uptime. This work constitutes an essential step toward a redefinition of the second of the International System of Units based on an optical transition.

光钟作为新一代时间频率标准，通过将本地振荡器频率精准参考至光频原子跃迁频率，具备更高的频率准确度和稳定度. 自二十一世纪初第一台全光学¹⁹⁹Hg⁺光钟成功问世以来，光学原子钟在近20余年里实现了跨越式发展. 当前顶尖光钟已实现10^-19量级的系统不确定度和频率稳定度，这一指标较传统微波原子钟提升了两个数量级以上，为基础物理研究和精密测量领域开辟了全新研究维度. 本文系统综述了光钟的研究进展，包括中性原子光钟与离子光钟的性能突破、新型光晶格囚禁技术的应用以及系统误差抑制方法的创新；同时重点探讨了光钟在驾驭国际原子时、降低基本物理常数可能的变化速率上限、检验爱因斯坦等效性原理等精密测量领域的前沿应用，为后续光钟技术的发展与应用拓展提供参考．

We present an International System of Units (SI)-traceable temperature calibration apparatus utilizing optical lattice clocks for precision metrology. The system employs a dual-blackbody radiation shield chamber with independent temperature control, enabling synchronous differential measurements of blackbody radiation (BBR)-induced frequency shifts in atomic ensembles. By correlating these shifts with chamber temperature, we propose absolute temperature determination traceable to the SI second through the optical clock frequency. Comprehensive uncertainty analysis demonstrates an absolute temperature uncertainty below 17 mK across the 200 − 350 K range based on Sr 87 optical lattice clock, representing an improvement of two orders of magnitude over current temperature measurements based on BBR-induced Rydberg state transitions. This advancement in primary thermometry offers significant improvements in precision, reproducibility, and versatility, with potential applications in metrology, fundamental physics, and industrial processes.