Compact 780-nm Rb optical clock
Phys. Rev. Applied 25, 014004 – Published 2 January, 2026
DOI: https://doi.org/10.1103/6pt5-zgmd
Abstract
We demonstrate a compact 780-nm rubidium optical clock, comprising an optical-frequency standard and an optical-frequency comb, with a total optical volume of 11.6 liters. Unlike the 778-nm rubidium atomic clocks based on two-photon transitions, the laser frequency in our system was stabilized to the hyperfine transition of (F = 2) → (F′ = 3) using modulation transfer spectroscopy. This approach effectively eliminates Doppler background and provides higher signal-to-noise ratio and sensitivity. After correcting for systematic perturbations, the absolute frequency was measured to be 384 228 115 200.7(2.7) kHz. A nearly 300-MHz microwave signal, whose phase exactly tracked that of the optical-frequency standard, was generated via the optical-frequency comb, yielding a frequency instability of 1.91 × at 1 s and 5.29 × at 1000 s in the electronic domain. The reproducibility was measured to be 3.66 × by comparing results from four independent daily measurements, each conducted following a complete system shutdown and restart. This is among the most precise frequency stabilization results for the first-excited-state transition of alkali metal atoms to date, and represents an optical clock based on this transition. This work offers a promising approach for the development of portable optical clocks.
