Clements Ethan R, Kim May E, Cui Kaifeng, Hankin Aaron M, Brewer Samuel M, Valencia Jose, Chen Jwo-Sy, Chou Chin-Wen, Leibrandt David R, Hume David B
National Institute of Standards and Technology, Boulder, Colorado 80305, USA.
Department of Physics, University of Colorado, Boulder, Colorado 80305, USA.
Phys Rev Lett. 2020 Dec 11;125(24):243602. doi: 10.1103/PhysRevLett.125.243602.
Laser decoherence limits the stability of optical clocks by broadening the observable resonance linewidths and adding noise during the dead time between clock probes. Correlation spectroscopy avoids these limitations by measuring correlated atomic transitions between two ensembles, which provides a frequency difference measurement independent of laser noise. Here, we apply this technique to perform stability measurements between two independent clocks based on the ^{1}S_{0}↔^{3}P_{0} transition in ^{27}Al^{+}. By stabilizing the dominant sources of differential phase noise between the two clocks, we observe coherence between them during synchronous Ramsey interrogations as long as 8 s at a frequency of 1.12×10^{15} Hz. The observed contrast in the correlation spectroscopy signal is consistent with the 20.6 s ^{3}P_{0} state lifetime and represents a measurement instability of (1.8±0.5)×10^{-16}/sqrt[τ/s] for averaging periods longer than the probe duration when dead time is negligible.
激光退相干通过展宽可观测的共振线宽并在时钟探测之间的死时间内添加噪声，限制了光钟的稳定性。关联光谱学通过测量两个原子系综之间的关联原子跃迁来避免这些限制，这提供了一种独立于激光噪声的频率差测量方法。在此，我们应用该技术对基于(^{27}Al^{+})中(^{1}S_{0}\leftrightarrow^{3}P_{0})跃迁的两个独立时钟进行稳定性测量。通过稳定两个时钟之间差分相位噪声的主要来源，我们在同步拉姆齐询问期间观察到它们之间长达8秒、频率为(1.12×10^{15})赫兹的相干性。在关联光谱信号中观察到的对比度与(20. — 6)秒的(^{3}P_{0})态寿命一致，并且当死时间可忽略不计时，对于平均周期长于探测持续时间的情况，代表了((1.8±0.5)×10^{-16}/\sqrt{τ/s})的测量不稳定性。
