Fig. 1. Energy level structure involved in ⁸⁷Sr optical clock

Fig. 2. Physical system of transportable optical clock. (a) Physical drawing; (b) three-dimensional drawing of MOT cavity and residual magnetic compensation coils

Fig. 3. Atomic clouds at different experimental stages. (a) Blue MOT atomic cloud after first stage of cooling; (b) red MOT atomic cloud after second stage of cooling; (c) separation between atoms not loaded into lattice and atomic cloud in lattice; (d) atomic cloud in lattice

Fig. 4. Atomic lifetime in one-dimensional optical lattice

Fig. 5. Direction of each beam in MOT cavity

Fig. 6. Clock transition spectra. (a) Spectrum with distinguishable sidebands; (b) degenerate spectrum with narrow linewidth

Fig. 7. Spin-polarized spectrum

Fig. 8. Rabi-flopping curve