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arxiv 1912.10218 v1 pith:PO6Q727D submitted 2019-12-21 quant-ph

Demonstration of a free space rubidium atomic clock with noise below the quantum projection limit

classification quant-ph
keywords atomicbelowfreelimitprojectionquantumatomsclock
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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A technique is demonstrated that allows free space atomic fountain clocks and interferometers to utilize optical cavity generated spin-squeezed states with over $390\,000$ ${}^{87}\text{Rb}$ atoms. Fluorescence imaging is used for population spectroscopy, after a free fall time of 4 milliseconds, to resolve a single-shot phase sensitivity of $814 (61)$ microradians, which is $5.8(0.6)$ decibels (dB) below the quantum projection limit. The dynamic range is observed to be 100 milliradians. When operating as a microwave atomic clock with $240\,000$ atoms at a 3.6 ms Ramsey time, a single-shot fractional frequency stability of $8.4(0.2)\times10^{-12}$ is reported, $3.8(0.2)$ dB below the quantum projection limit.

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