Atomic clock engineering

—by Aidan Strathearn

Incorporating realistic optical models that include wavefront curvature into a detailed atomistic model of atomic beam clocks reveals systematic offsets to resonant frequencies important for developing high-accuracy portable clocks.

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, and as such have many useful applications in sensing, metrology and navigation.  A major challenge in deploying atomic clocks for these uses is to maintain the precision and stability achieved in lab-scale experiments while engineering the devices to be compact and portable.

Enhancing performance with laser focus

Recently, under the supervision of Chief Investigator Prof. Tom Stace and in collaboration with the group of Andre Luiten at The University of Adelaide, I performed detailed modelling and simulations for a particular type of compact atomic clock—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 then allows the atomic transition frequency that defines the clock to be extracted.

One concern for these devices is that performance will be affected by the beam profile of the laser.  In our work (https://arxiv.org/abs/2212.00308), we elucidate the adverse effects of using a realistic laser with curved wavefronts, ultimately showing that there is a way to focus the laser to reduce these effects and achieve optimal clock performance.

From theory to real atomic clock experiments

Having previously worked only on purely theoretical problems, where cows are spherical and exist in a vacuum, I found it a tricky exercise digging through the gory details of real atomic clock experiments to perform realistic simulations.  However, the experience was rewarding, furthering my appreciation and respect for the work undertaken by my experimentalist colleagues.

Aidan Strathearn is a Research Fellow at UQ, working under the supervision of Chief Investigator Tom Stace.  He obtained his PhD on tensor networks and non-Markovian quantum dynamics from the University of St Andrews in September 2020.  His research focuses on quantum devices strongly coupled to their environment leading to such effects as non-Markovian decoherence, dissipative phase transitions and non-canonical equilibrium states.  As part of EQUS’ Quantum Clock Flagship, Aiden is aiming to devise more detailed and improved models for atomic clocks that will inform future design engineering.