Quantum Projection Noise in an Atomic Fountain: A High Stability Cesium Frequency Standard
نویسندگان
چکیده
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 N 21y2 at law of atomic projection noise. With 6 3 105 atoms, the relative frequency stability is 4 3 10214t21y2, where t is the integration time in seconds. This is the best short-term stability ever reported for primary frequency standards, a factor of 5 improvement over previous results. [S0031-9007(99)09299-6]
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