Cancellation of Doppler shifts in a cold-atom CPT clock

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.