Miniature atomic clocks based on coherent population trapping (CPT) states in thermal atoms are emerging as an important component in many field applications, particularly where satellite frequency standards are not accessible. Cold-atom CPT clocks promise improved accuracy and stability. Here we demonstrate a cold-atom CPT clock using a high-contrast double-lambda CPT configuration. Doppler frequency shifts are explained using a simple model and canceled by interro- gating the atoms with counterpropagating light beams. We realize a compact cold-atom CPT clock with a fractional frequency stability of 4 x 10-11/√τ, thus demonstrating the promise of these devices. We also show that the long-term stability is currently limited by the second-order Zeeman shift to 2x10-12 at 1000s.
Citation: Physical Review A
Pub Type: Journals
Atomic Clocks, Coherent Population Trapping, Doppler Shift