A cold atomic clock capable of operating in space is presented in Nature Communications this week. The findings demonstrate that cold atoms can be used as stable in-orbit clocks and may lead to uses in metrology and for testing some of the fundamental principles of physics.

The timing of an atomic clock is based on the energy difference between two atomic levels. This energy difference in cold atoms can be measured precisely by using lasers and clocks can remain stable against external perturbations under laboratory conditions. However, long term operation of such clocks in space is challenging because the environmental field and high energy particles from the Earth’s radiation belt interfere with the clock stability.

Liang Liu and colleagues report evidence of the stable in-orbit operation of a cold atomic clock. The authors trap and cool rubidium atoms and probe them using microwave and laser pulses in the microgravity environment. They detect the atomic population after microwave interrogation and find the stability of the in-orbit clocks to be three parts in ten trillion.

These robust and stable cold atomic clocks in harsh and microgravity environments could be used to develop space based sensors for metrology and to test variation of fundamental constants, general relativity and violations of Einstein’s equivalence principle.