Optical clocks are the most precise measurement devices. Here we experimentally characterize one such clock based on the ¹S₀-³P₀ transition of neutral ¹⁷¹Yb atoms confined in an optical lattice. Given that the systematic evaluation using an interleaved stabilization scheme is unable to avoid noise from the clock laser, synchronous comparisons against a second ¹⁷¹Yb lattice system were implemented to accelerate the evaluation. The fractional instability of one clock falls below 4 × 10⁻¹⁷ after an averaging over a time of 5,000 seconds. The systematic frequency shifts were corrected with a total uncertainty of 1.7 × 10⁻¹⁶. The lattice polarizability shift currently contributes the largest source. This work paves the way to measuring the absolute clock transition frequency relative to the primary Cs standard or against the International System of Units (SI) second.

We report on the absolute frequency measurement of the 6 s ^{2 1} S ₀ –6 s 6 p ³ P ₀ transition in ¹⁷¹ Yb with a fractional uncertainty of 7.3 × 10 ^–16 . A global positioning system carrier phase frequency transfer was established between National Institute of Metrology of China and East China Normal University, which linked the optical frequency of the ECNU Yb1 clock to the second in the International System of Units (SI) through international atomic time. Frequency measurements were carried out in 15 separate days with a total time over 3.8 × 10 ⁵ s. The absolute frequency was determined to be 518 295 836 590 863.30(38) Hz. Our result is in good agreement with the recommended value in neutral Yb as a secondary representation of the SI second endorsed by the International Committee for Weights and Measures.

A three-axis atomic magnetometer for nuclear magnetic resonance gyroscopes (NMRGs) is demonstrated. To satisfy the miniaturization demand of NMRGs, a magnetic-resonance-based atomic magnetometer is used to detect the longitudinal magnetic field. Simultaneously, the longitudinal field is modulated to measure the magnetic field in x and y axes based on a nonlinear magneto-optical rotation magnetometer. Magnetic field sensitivities of 100 fT/Hz^1/2 in x and y axes and 20 fT/Hz^1/2 in the z axis are achieved. The bandwidths of this magnetometer are 96 Hz in x and y axes and 6 Hz in the z axis. A high-sensitivity three-axis magnetometer is essential to accomplish the rotation detection in NMRGs and also plays a vital role in optimizing the performance of gyroscopes.

The optical atomic clocks have the potential to transform global timekeeping, relying on the state-of-the-art accuracy and stability, and greatly improve the measurement precision for a wide range of scientific and technological applications. Herein we report on the development of the optical clock based on ¹⁷¹Yb atoms confined in an optical lattice. A minimum width of 1.92-Hz Rabi spectra has been obtained with a new 578-nm clock interrogation laser. The in-loop fractional instability of the ¹⁷¹Yb clock reaches 9.1 × 10⁻¹⁸ after an averaging over a time of 2.0 × 10⁴ s. By synchronous comparison between two clocks, we demonstrate that our ¹⁷¹Yb optical lattice clock achieves a fractional instability of 4.60 × 10 − 16 / τ .

We report modulation-transfer spectroscopy (MTS) on the $6\mathit{s}6\mathit{p}{}^{3}P_0\leftrightarrow 6\mathit{s}7\mathit{s}{}^{3}S_1$ transition in neutral ytterbium (Yb) isotopes in a hollow cathode lamp. The MTS dispersive signals show an effective linewidth of 70 MHz, contributed primarily by the pressure broadening. MTS has demonstrated the capability of completely resolving all isotopic lines, except the one in low-abundance ${}^{168}\mathrm{Yb}$. Frequency measurements of the isotope-stabilized laser are performed using an optical comb, and systematic shifts therein are corrected. We have examined the relative isotope shifts, and the hyperfine constants for the $6\mathit{s}7\mathit{s}{}^{3}S_1$ state are given as $\mathit{A}\left({}^{171}\mathrm{Yb}\right)=6837.83\left(19\right)$ MHz, $\mathit{A}\left({}^{173}\mathrm{Yb}\right)=-1891.46\left(7\right)$ MHz and $\mathit{B}\left({}^{173}\mathrm{Yb}\right)=-0.62\left(16\right)$ MHz. Our results are in reasonable agreement with previously reported values and essentially resolve the existing discrepancies.