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Large scale ab initio calculations of the electric contribution (i.e. the electric field gradient) to the electric quadrupole hyperfine interaction constants $B$ for the $5p~^2P_{3/2}$ state in $^{109}$Cd$^+$ ion and the $5s5p~^3P_{1,2}$ states in neutral $^{109}$Cd atom were performed. To probe the sensitivity of $B$ to different electron correlation effects, six sets of variational multi-configuration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. The calculated electric field gradients, together with experimental values of $B$, allow us to extract a new value of the nuclear electric quadrupole moment $Q$($^{109}$Cd) = 0.634(22) b which is about 5\% larger than the recommended value [Stone, At. Data Nucl. Data Tables 111-112, 1 (2016); Pyykk\"{o}, Mol. Phys. 116, 1328 (2018)]. Efforts were made to provide a realistic theoretical uncertainty for the final $Q$ value based on statistical principles and correlation with the magnetic dipole hyperfine interaction constant $A$., Comment: 15 pages,2 figures. arXiv admin note: text overlap with arXiv:1906.08465

In the weak-magnetic-field approximation, we calculated the hyperfine-induced Lande g -factors of the 3 P 0 o clock states in 27 Al + and 87 Sr by using the multi-configuration Dirac–Hartree–Fock method. The present results, δ g hfs ( 1 ) ( 3 P 0 o ) = − 1.183 ( 6 ) × 10 − 3 for 27 Al + and δ g hfs ( 1 ) ( 3 P 0 o ) = 7.78 ( 30 ) × 10 − 5 for 87 Sr, agree with experimental values very well. The influence of relativistic effects and electron correlations on the involving hyperfine interaction and Zeeman matrix elements, and energy separations were investigated in detail. We also estimated the contributions from perturbing states to the g -factors concerned so as to truncate the summation over the perturbing states without loss of accuracy. Based on these, the computational uncertainties were systematically analyzed for the hyperfine-induced Lande g -factors of the 3 P 0 o clock states in these two atomic systems.

The work presented in this paper is based on an optical frequency comb injection-locking, active filtering and amplification method to build a narrow linewidth laser for second cooling of the strontium atoms in an optical lattice clock. An optical femtosecond laser comb with mode spacing of 250 MHz as master laser is applied to directly inject into an external cavity semiconductor laser at 689 nm called slave laser, a single mode is selected and amplified from the optical femtosecond laser comb.

In the ultra-cold 87Sr atomic system, the Zeeman shift of the clock transition was measured with the σ±-polarized interrogation to accurately determine the g-factors of the 5s2 1S0 and 5s5p 3P0 states.

We presented experimental and theoretical studies of the effect of an external magnetic field on the forbidden transition in the bosonic Sr atom. In our ultra-cold atomic system, the excitation fraction of $5s5p$~$^3P_0$~-~$5s^2$~$^1S_0$ forbidden transition was measured under the circumstance of the different magnetic field strengths by using the normalized detection method. Based on perturbation theory, we calculated the magnetic-field-induced $5s5p$~$^3P_0$~-~$5s^2$~$^1S_0$ transition rate. The excitation fraction as a function of the magnetic field strength was deduced according to the calculated results. A good agreement was found between the experimental measurements and the calculations. This study should be helpful in evaluating the magnetic field effects on the forbidden transition rate with higher accuracy. Moreover, it can help to understand the ultra-cold atomic interaction in the external magnetic field., 17 pages, 4 figures, 055017

At present the optical clock with accuracy and stability achieves to 10-18 level, which could be the next generation of time and frequency standard. This paper gives an introduction of the progress of researching on the optical lattice clock of Strontium atom in NTSC (National Time Service Center). We realize the (5s5s)1S0—(5s5p)1P1 cooling (blue MOT) and (5s5s)1S0—(5s5p)3P1 cooling (red MOT) in succession for the optical lattice clock, and loading these cold atoms in a lattice composed by a magic wave-length is studied. By using our narrow line-width diode laser and the fiber femtosecond optical frequency comb, we precisely measure the absolute frequencies of the inter-combination transitions (5s5s)1S0—(5s5p)3P1 of four isotopes of Strontium referenced to an H maser.

We report on frequency measurement of the intercombination (5s2)1S0–(5s5p)3P1 transition of the four natural isotopes of strontium, including 88Sr (82.58%), 87Sr (7.0%), 86Sr (9.86%), and 84Sr (0.56%). A narrow-linewidth laser that is locked to an ultra-low expansion (ULE) optical cavity with a finesse of 12000 is evaluated at a linewidth of 200 Hz with a fractional frequency drift of 2.8×10−13 at an integration time of 1 s. The fluorescence collector and detector are specially designed, based on a thermal atomic beam. Using a double-pass acousto-optic modulator (AOM) combined with a fiber and laser power stabilization configuration to detune the laser frequency enables high signal-to-noise ratios and precision saturated spectra to be obtained for the six transition lines, which allows us to determine the transition frequency precisely. The optical frequency is measured using an optical frequency synthesizer referenced to an H maser. Both the statistical values and the final values, including the corrections and uncertainties, are derived for a comparison with the values given in other works.