New applications of atomic clocks for precision measurement

In recent years the performance of atomic clocks has been improved to an unprecedented level. In particular, for lattice clocks based on neutral atoms, the instability has reached an order of magnitude around 10^-19, and the uncertainly at the low 10^-18 level, so their applications in precision measurement have been pushed to a new level. Apart from their use in measuring the variation of the fine structure constant, detecting gravitational waves, and hunting for dark matter, highly accurate optical clocks are also a powerful tool for geodesy and verification of general relativity. Here we give an introduction to the application of lattice clocks for geodesy from the viewpoint of gravitational redshift measurements. In the future, measurement of a system’s entropy with highly accurate lattice clocks could be a new research area for precision measurement.