We measured the absolute frequency of the 1 S0-3 P0 transition of 171 Yb atom confined in a one-dimensional optical lattice relative to the SI second. The determined frequency was 518 295 836 590 863.38(57) Hz. The uncertainty was reduced by a factor of 14 compared with our previously reported value in 2013 due to the significant improvements in decreasing the systematic uncertainties. This result is expected to contribute to the determination of a new recommended value for the secondary representations of the second. 2 Optical clocks have made remarkable progress in the last decade, and some of them have already surpassed the best accuracy of Cs microwave clocks by two orders of magnitude. 1-4) Accordingly, a redefinition of the SI second, which is currently based on a microwave transition of Cs atom, has been seriously considered by using optical clocks. 5-7) 171 Yb optical lattice clocks are one of the best developed optical lattice clocks which have an advantage of lower quantum projection noise than single trapped-ion clocks, and are being investigated vigorously by several research groups around the world. [8][9][10][11][12][13][14][15][16] The frequency of the 1 S0-3 P0 transition of 171 Yb has been included in the secondary representation of the SI second by the International Committee for Weights and Measures (CIPM2015) 17) using the reported values of the absolute frequency measurements. 8-11, 18, 19) Since 2015, two more measurement values were reported which will contribute to a new determination of the recommended frequency value in the future. 12,20) Since the first absolute frequency measurement of the Yb lattice clock at KRISS (Korea Research Institute of Standards and Science), 10) there have been significant improvements to reduce the systematic uncertainty. The details of the experiment were reported previously 10,21,22) , thus, they will be described only briefly in this article emphasizing the systematic improvements thereafter. The singlet transition ( 1 S0-1 P1) at 399 nm was used for the Zeeman slowing and the first stage magneto-optical trap (MOT) with the temperature of about 1 mK. The atoms were further cooled to about 20 μK by the second stage MOT using the triplet transition ( 1 S0-3 P1) at 556 nm. Next, the atoms were transferred to a verticallyoriented 1D optical lattice trap at the magic wavelength at 759 nm, and were spin-polarized alternatively to either one of the two magnetic sublevels of the ground state ( 1 S0) by optical pumping using 1 S0-3 P1 transition at 556 nm and the bias magnetic field of 0.275 mT.The optical lattice was formed by a build-up cavity (finesse ~220) to enhance the maximum lattice trap depth (U0) up to ~2500 Er, where Er is the recoil energy. The polarization of the lattice laser was filtered by a thin-film linear polarizer which was placed between two cavity mirrors as a folding mirror. The extinction ratio was enhanced to more than 1:10,000 by the cavity. The frequency of the lattice laser was stabilized to a fiber frequency comb and monitored with a...

Advanced satellite-based frequency transfers by two-way carrier-phase (TWCP) and integer precise point positioning have been performed between the National Institute of Information and Communications Technology and Korea Research Institute of Standards and Science. We confirm that the disagreement between them is less than at an averaging time of several days. In addition, an overseas frequency ratio measurement of Sr and Yb optical lattice clocks was directly performed by TWCP. We achieved an uncertainty at the mid-10 level after a total measurement time of 12 h. The frequency ratio was consistent with the recently reported values within the uncertainty.

We demonstrate that the differential ac-Stark shift of a Zeeman-sensitive ground hyperfine transition in an optical trap can be eliminated by using properly polarized trapping light. We use the vector polarizability of an alkali-metal atom to produce a polarization-dependent ac-Stark shift that resembles a Zeeman shift. We study a transition from the |2S1/2,F=2,mF=-2> to the |2S1/2,F=1,mF=-1> state of 7Li to observe 0.59±0.02  Hz linewidth with interrogation time of 2 s and 0.82±0.06  s coherence time of a superposition state. Implications of the narrow linewidth and the long coherence time for precision spectroscopy and quantum information processing using atoms in an optical lattice are discussed.

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We report a measurement of the absolute frequency of the 1S0–3P0 transition in the 171Yb optical lattice clock at KRISS (KRISS-Yb1) for 14 months, which was referenced to the SI second by primary and secondary standards worldwide via International Atomic Time. The determined absolute frequency is 518 295 836 590 863.75(14) Hz with the relative frequency uncertainty of 2.6 × 10−16, which agrees well with other reports. This result is expected to contribute to the future update of the CIPM recommendation frequency of the secondary frequency standards.