Testing gravitational redshift based on microwave frequency links onboard the China Space Station

Abstract

In November 2022, the China Space Station (CSS) was equipped with a cold atomic microwave clock and a Sr optical lattice clock with stabilities of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}/\sqrt{\ensuremath{\tau}}$ and $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}/\sqrt{\ensuremath{\tau}}$ (where $\ensuremath{\tau}$ is the integration time in seconds), respectively, which provides an excellent opportunity to test gravitational redshift (GRS) with higher accuracy than previous results. Based on high-precision frequency links between the China Space Station and a ground station, we formulated a model and provided simulation experiments to test GRS. Simulation results suggest that this method could test the GRS at the accuracy level of $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$, more than 2 orders in magnitude higher than the result of the experiment of a hydrogen clock on board a flying rocket more than 40 years ago.