A cold-atom beam clock based on coherent population trapping

We present results from an atomic clock that employs a beam of cold ⁸⁷Rb atoms and spatially separated (Ramsey) coherent population trapping interrogation of the hyperfine clock transition at 6.834 GHz. The cold atomic beam is generated through the use of a 2D⁺-magnetooptical trap. The interrogation is performed on the D2 line of ⁸⁷Rb, and the optical fields use a counter-propagating ${\sigma }_{+}-{\sigma }_{-}$ probing scheme. The use of cold atoms allows for relatively narrow Ramsey fringes even for a small spatial separation between the two interrogation zones(4.6 cm). The resulting clock has a short-term stability of $3\times {10}^{-11}/\sqrt{\tau }$ .