Realisation of a Frequency Standard Using an Atomic Fountain *

An experimental study of intermodulation effects in an atomic fountain frequency standard

Cesium Atomic Fountain Clocks at Nmij

We describe the recent progress in our cesium atomic fountains at National Metrology Institute of Japan (NMIJ). We have developed three atomic fountains: NMIJ-F1, NMIJ-F2, and a truncated atomic beam fountain. NMIJ-F1 has been the primary frequency standard with uncertainty of 4×10 -15 since 2004. Especially in the last 4 years, we have reported the data to Bureau International des Poids et Mes...

Quantum Projection Noise in an Atomic Fountain: A High Stability Cesium Frequency Standard

We describe the operation of a laser cooled cesium fountain clock in the quantum limited regime. An ultrastable cryogenic sapphire oscillator is used to measure the short-term frequency stability of the fountain as a function of the number of detected atoms Nat. For Nat varying from 4 3 104 to 6 3 105 the Allan standard deviation of the frequency fluctuations is in excellent agreement with the ...

Initial atomic coherences and Ramsey frequency pulling in fountain clocks

In the uncertainty budget of primary atomic cesium fountain clocks, evaluations of frequency-pulling shifts of the hyperfine clock transition caused by unintentional excitation of its nearby transitions (Rabi and Ramsey pulling) have been based so far on an approach developed for cesium beam clocks. We re-evaluate this type of frequency pulling in fountain clocks and pay particular attention to...

Measurement of dynamic end-to-end cavity phase shifts in cesium-fountain frequency standards.

We have measured a previously unobserved systematic frequency shift in our cesium-fountain frequency standard, NIST-F1. This shift, predicted theoretically previously, mimics the well-known end-to-end phase shift in atomic beam standards when synchronous thermal transients are present. Detuning the microwave cavity several megahertz from resonance reduces this effect to the deltaf/f = 1o(-16) l...