An optical lattice clock

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 technique, which established a coherent link between optical and radio frequencies, optical clocks have attracted increasing interest as regards future atomic clocks with superior precision. To date, single trapped ions and ultracold neutral atoms in free fall have shown record high performance that is approaching that of the best Cs fountain clocks. Here we report a different approach, in which atoms trapped in an optical lattice serve as quantum references. The 'optical lattice clock' demonstrates a linewidth one order of magnitude narrower than that observed for neutral-atom optical clocks, and its stability is better than that of single-ion clocks. 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.

Optical Lattice Polarization Effects on Hyperpolarizability of Atomic Clock Transitions

“…On the way to this goal it will be necessary to use new approaches and to solve step-by-step the critical physical problems [2]. For example, since at the magic wavelength λ m the first-order shift vanishes, one of the main factors that limits the accuracy of these optical clocks is the second-order shift due to the atomic hyperpolarizability.…”

“…The crucial ingredient, for achieving such high metrological performance, is the existence of the magic wavelength λ m , at which the first-order (in intensity) light shift of the clock transition 1 S 0 → 3 P 0 cancels for alkaline-earth-like atoms (such as Mg, Ca, Sr, Yb, Zn, Cd). To date in several experiments cold atoms were trapped in optical lattices at the magic wavelength and the clock transition was observed [2,4,5,6]. From the metrological viewpoint even isotopes (with zero nuclear spin) are more attractive.…”

“…where terms β (1,2) e are related to the resonance twophoton transitions (6s6p) 3 P 0 →(6s8p) 3 P 0,2 at the doubled magic frequency 2ω m , and β (3,4) e originate from the interaction of the level (6s6p) 3 P 0 with the other levels (6s6p) 3 P 1,2 of the same fine-structure manifold. The polarization dependencies for β (1,2) e are determined by P 0,2 (e), whereas for β (3,4) e are determined by Q 1,2 (e).…”

“…In recent years significant attention has been devoted to optical lattice atomic clocks [1,2], in part because the prospects for a fractional frequency uncertainty of such a clock could achieve of the level 10 −17 -10 −18 . Apart from obvious practical applications, such improved clocks will be critical for a variety of terrestrial and space-borne applications including improved tests of the basic laws of physics and searches for drifts in the fundamental constants [3].…”

“…For example, since at the magic wavelength λ m the first-order shift vanishes, one of the main factors that limits the accuracy of these optical clocks is the second-order shift due to the atomic hyperpolarizability. Indeed, for the formation of optical lattices with the potential depth of order of MHz [2,4,5,6] it is necessary to use laser beams with the intensity at a level of a few tens of kW/cm 2 . According to our numerical estimates for different alkaline-earth-like atoms [8,9] and first experimental observations for Sr [6], the second-order shift can be at a level of 1-10 Hz in such high-intensity fields.…”