Measuring the effect of gravitational frequency shift doubling using a hydrogen clock-based quantum level

The effect of gravitational frequency shift doubling in a system of stationary and transported hydrogen quantum clocks in the Earth's gravitational field has been measured for the first time with an instability of 1 $\cdot$ 10$^{-15}$. The clocks were separated in height by 34 m and connected by a radio channel based on optical fiber. The measured relative doubled “redshift” effect at this altitude was $\Delta f_{GR}/f_{ref}$ = (-7.73 $\pm$ 1.61) $\cdot$ 10$^{-15}$.