Fig. 1. The principle of the generation of optical frequency standard

Fig. 2. (a) Measurement of the gravitational frequency shift between the two groups of atoms in a one-dimensional optical lattice along the gravitational direction ^[29]; (b) Measurement of the gravitational frequency shift between two optical lattice atomic clocks at different vertical heights ^[41]

Fig. 3. (a) Measurements of the naked Rabi frequency^[48]; (b) Measurement of the laser intensity distribution^[48] (c) The setup for determining the lifetime of the metastable state by measuring the electric dipole matrix element^[48]

Fig. 4. (a) Principle of the dual-excitation spectrum technology for clock transition detection^[51]; (b) Measurement of the differential coefficient of the tensor AC Stark shift using the dual-excitation spectrum^[51]; (c) The measurement precision beyond the Dick limit^[51]; (d) Frequency difference of tensor AC Stark shifts between |mF|=9/2→|mF|=9/2 and |mF|=7/2→|mF|=7/2 transitions^[51]