Ultracold Atoms for Ultrastable Frequency Standards

А. В. Тайченачев, Valeriy I. Yudin, Sergei N Bagayev

Sterr, Degenhardt, Stoehr +3 more

Roberto Onofrio, Luca Salasnich

Ksenia Yu. Khabarova, Sergey N. Slyusarev, S A Strelkin +4 more

A laser system with a narrow generation line for secondary laser cooling of 87 Sr atoms has been developed and investigated. It is planned to use ultracold 87 Sr atoms loaded in an optical lattice in an optical frequency standard. To this end, a 689-nm semiconductor laser has been stabilised using an external reference ultrastable cavity with vibrational and temperature compensation near the critical point. The lasing spectral width was 80 Hz (averaging time 40 ms), and the frequency drift was at a level of 0.3 Hz s -1 . Comparison of two independent laser systems yielded a minimum Allan deviation: 2 × 10 -14 for 300-s averaging. It is shown that this system satisfies all requirements necessary for secondary cooling of 87Sr atoms using the spectrally narrow 1 S 0 — 3 P 1 transition (λ = 689 nm).

V. D. Ovsyannikov, Vitalii G Pal'chikov, Hidetoshi Katori +1 more

The theoretical aspects of the Stark spectroscopy of cold alkaline-earth atoms in a three-dimensional optical lattice related to the development of ultrastable optical frequency standards of a new generation are considered. The main attention is devoted to the dispersion and polarisation properties of the light frequency shift in these atoms, which depend on the power, frequency, and polarisation of lasers forming the optical lattice. The 'light-shift-cancellation' regime is considered in detail, in which the second-order dynamic Stark shifts at the forbidden clock 3 P 0 — 1 S 0 and 3 P 1 — 1 S 0 transitions are mutually compensated. The wavelengths at which this regime takes place ('magic' wavelengths) are calculated for the He, Be, Mg, Ca, Sr, Yb, and Hg atoms. The fourth-order dynamic susceptibilities (hyperpolarisabilities) are calculated for Sr atoms and the contribution of higher-order multipole corrections to the dynamic polarisability of the 3 P 0 and 1 S 0 levels is estimated.