Atomic clocks exploit the identical transition frequencies of atoms of the same species to provide reproducible frequency standards, with such success that the SI definition of one second is based on a particular transition of caesium atoms.

Time and frequency measurements made using atomic clocks are outstandingly precise, routinely reaching precisions of one part in 10¹⁸ or so. As such, they have many applications in sensing, metrology and navigation. A major challenge in deploying atomic clocks for these uses is maintaining the high precision and stability achieved in laboratory-scale experiments while engineering the devices to be compact and portable.

In 2023, Research Fellow Aidan Strathearn and Chief Investigator Tom Stace incorporated realistic optical models into a model of atomic beam clocks .

They performed detailed modelling and simulations for a compact atomic clock called a Ramsey–Borde interferometer, to investigate how its performance could be optimised.

In this type of clock, atoms are manipulated using a laser in a way that causes quantum interference between their internal states. Measurement of the resulting interference fringes may be used to extract the atomic transition frequency that defines the clock. One concern for these devices is that performance will be affected by the beam profile of the laser.

The team showed that using a realistic laser, with curved wavefronts, leads to systematic offsets to the resonant frequencies of the clock, which adversely affect its performance. However, they also demonstrated a way of focusing the laser to reduce these effects and achieve optimal clock performance.

This story was first published in the 2023 EQUS annual report, and was written by Kristen Harley.