Ramsey resonance in a zacharias fountain

摘要: We report a realization of Zacharias's 1953 proposal for observing Ramsey resonance in an atomic fountain. Launched upward from moving optical molasses where they have been cooled to ~ 5 ?K, cesium atoms pass once through microwave cavity, continue the summit their trajectory, then fall again same completing separated-fields interaction. The spend 0.25 s free flight above cavity. Linewidth (2 Hz) and S/N imply stability 3?10-12 ?-1/2, at least as good existing Cs clocks, with eventual expected improvements 102.