Miniature atomic clocks based on coherent population trapping (CPT) states in thermal atoms are an important component in many field applications, particularly where satellite frequency standards are not accessible. Cold-atom CPT clocks promise improved accuracy and stability over existing commercial technologies. Here we demonstrate a cold-atom CPT clock based on 87 Rb using a high-contrast double-configuration. Doppler frequency shifts are explained using a simple model and canceled by interrogating the atoms with counterpropagating light beams. We realize a compact cold-atom CPT clock with a fractional frequency stability of 4 × 10 −11 τ −1/2 , thus demonstrating the potential of these devices. We also show that the long-term stability is currently limited by the second-order Zeeman shift to 2 × 10 −12 at 1000 s.
We decelerated an atomic beam of 87 Rb using a stimulated-emission slowing technique that employs a bichromatic standing light wave of high intensity, and increased the atom number in a magneto-optical trap (MOT) of low capture velocity by up to a factor of 14, and the load rate into the MOT by a factor of 20. We performed the slowing over distances under 1.5 cm with 5.2 mW of total power in the bichromatic beams. The average stimulated force was 2.2 times the maximum spontaneous emission force, and could be made even stronger in a smaller apparatus.
A compact cold-atom clock based on coherent population trapping (CPT) is being developed. Long-term goals for the clock include achieving a fractional frequency accuracy of 1×10 -13 in a package of less than 10 cm 3 in volume.Here we present an overview of a prototype clock design, and a systematic evaluation of the first-order Doppler shift. We also introduce our second-generation physics package.
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