Simulation Test of Gravitational Redshift by Microwave Links of China Space Station

  Objectives  Gravitational redshift test using high precision space-borne/sattelite-payload atomic clocks is always a hot topic in physics. With the improvement of the accuracy of atomic clocks, it is possible to use high-precision time-frequency signals to test the gravitational redshift and determine the gravitational potential.

  Methods  The experiment module of China space station (CSS) is expected in orbit in October 2022, which lays a foundation for high-precision gravitational redshift experiment. The dual-frequency combination method is applied to eliminate the propagation frequency shifts by using an uplink and a downlink with the same frequency and different polarization direction. The gravitational redshift simulation experiment is carried out by using the microwave links of CSS time-frequency comparison system.

  Results  The results show that the stability of atomic clock achieves $\mathrm{2}\times {\mathrm{10}}^{-\mathrm{15}}/\sqrt[]{\tau }$, the long term stability reaches 10^-18, and the accuracy of gravitational redshift reaches 10^-7.

  Conclusions  It is 1-2 orders of magnitude higher than the highest accuracy of gravitational redshift in the world.