Cryogenic optical lattice clocks
Ichiro Ushijima, Masao Takamoto, Manoj Das, Takuya Ohkubo & Hidetoshi Katori
Nature Photonics 9, 185–189 (2015) doi:10.1038/nphoton.2015.5
Received 13 May 2014 Accepted 06 January 2015 Published online 09 February 2015
The accuracy of atomic clocks relies on the superb reproducibility of atomic spectroscopy, which is accomplished by careful control and the elimination of environmental perturbations on atoms. To date, individual atomic clocks have achieved a 10−18 level of total uncertainties1, 2, but a two-clock comparison at the 10−18 level has yet to be demonstrated. Here, we demonstrate optical lattice clocks with 87Sr atoms interrogated in a cryogenic environment to address the blackbody radiation-induced frequency shift3, which remains the primary source of systematic uncertainty2, 4, 5, 6 and has initiated vigorous theoretical7, 8 and experimental9, 10 investigations. The systematic uncertainty for the cryogenic clock is evaluated to be 7.2 × 10−18, which is expedited by operating two such cryo-clocks synchronously11, 12. After 11 measurements performed over a month, statistical agreement between the two cryo-clocks reached 2.0 × 10−18. Such clocks’ reproducibility is a major step towards developing accurate clocks at the low 10−18 level, and is directly applicable as a means for relativistic geodesy13.