Chasing stability in chip-scale atomic beam clocks

We report on our progress in developing chip-scale atomic beam clocks for timing holdover applications. Our approach is based on a chip-scale, Rb atomic beam platform using etched collimator structures [1] integrated into a compact, passively pumped device [2]. The clock signal is realized using Ramsey coherent population trapping (CPT) spectroscopy over a 1 cm distance with fractional frequency instability below 1 × 10-9 at 1 s of integration. We present a detailed characterization of systematics in this system arising from the finite Doppler width inherent in a compact beam geometry, the associated impact on resonant and off-resonant light shifts, and other key systematics which we control at the 10-12 level for integration times exceeding 104 s. Miniaturization efforts for the full clock system will be presented as well as an outlook for week-scale stability which could be achieved in this system [1] Li et al., "Cascaded collimator for atomic beams traveling in planar silicon devices," Nat Commun 10, 1831 (2019). [2] Martinez et al. “A chip-scale atomic beam clock,” Nat Commun 14, 3501 (2023).