An optical lattice clock

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Abstract
The precision measurement of time and frequency is a prerequisite not only for fundamental science but also for technologies that support broadband communication networks and navigation with global positioning systems (GPS). The SI second is currently realized by the microwave transition of Cs atoms with a fractional uncertainty of 10-15 (ref. 1). Thanks to the optical frequency comb technique2,3, which established a coherent link between optical and radio frequencies, optical clocks4 have attracted increasing interest as regards future atomic clocks with superior precision. To date, single trapped ions4,5,6 and ultracold neutral atoms in free fall7,8 have shown record high performance that is approaching that of the best Cs fountain clocks1. Here we report a different approach, in which atoms trapped in an optical lattice serve as quantum references. The ‘optical lattice clock’9,10 demonstrates a linewidth one order of magnitude narrower than that observed for neutral-atom optical clocks7,8,11, and its stability is better than that of single-ion clocks4,5. The transition frequency for the Sr lattice clock is 429,228,004,229,952(15) Hz, as determined by an optical frequency comb referenced to the SI second.