ELIMINATING COLD-COLLISION FREQUENCY-SHIFTS

A technique to cancel the frequency shift due to cold collisions of la ser-cooled atoms is proposed. Results for future clocks based on Cs-13 5 and Cs-137 are presented. We find a Cs-137 fountain clock can be ope rated with no cold-collision shift by adjusting the population ratios in the fountain, and it may also be possible for Cs-135. This techniqu e can also be applied to other phase-sensitive measurements using cold atoms, including atom interferometers.