Over the last decade, miniature instruments based on microfabricated alkali vapor cells have emerged as a compelling technology for achieving small size and low-power operation while retaining much of the high precision afforded by the use of atomic spectroscopy. Chip-scale atomic clocks1 are now a commercial reality2 and achieve frequency instabilities below 10???11 at one hour of integration while consuming only 120 mW of power, 30 times less than any pre-vious commercial atomic clock. This improvement in the power consumption is enabled mainly by the use of a vertical-cavity surface emitting laser as the light source and by the small size and good thermal isolation of the physics package.
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