Integrated cold-atom microwave clock

Precision frequency and timing are technologies built into modern society, driving telecommunications, network synchronisation, navigation, cyber security, and financial trading. The near ubiquitous availability of low-cost and high-quality timing through quartz oscillators and GPS timing means that the technology is hidden in plain sight.

Microwave atomic clocks have represented the state of the art since the 1950s, operating in two regimes for measuring an atomic hyperfine transition: either direct interrogation or Ramsey spectroscopy. The former is the approach widely used in the atomic clocks for global navigation satellite systems (GNSS) whereas the latter is a more sophisticated technique used in terrestrial beam clocks and atomic fountains.

The technological challenge remains to create microwave atomic clocks that are compact, portable, and can be deployed in various environments relevant to defence and security, rather than being confined to a laboratory. The holy grail in microwave clocks is for atomic fountain performance in a shoebox, or smaller. The field has begun to see the use of compact laser cooling platforms towards commercial atomic clocks.

Initial results show short-term stability better than 1e-12 per-root-second, integrating to a fractional instability of 3e-15 at a day, which is maintained for periods longer than a week. Under laboratory conditions and assuming perfect calibration, this corresponds to a contribution to synchronisation error budgets of 50 ns per day, comparable to a level of synchronisation accuracy which is currently only achievable when platforms have access to GNSS or similar high-footprint infrastructure.

Where microwave atomic clocks have an advantage over their optical counterparts is the simplicity and reliability of their construction, resulting in more rapidly deployable technologies.

At Strathclyde, parallel research strands have built over the last decade that focus on developing integrated cold atom platforms, and microwave atomic clocks and frequency references. The culmination of this work has been the recent demonstrations of cooling and interrogating of atoms within a microwave cavity and of an atomic fountain on a gMOT chip, enabling Ramsey times up to 100 ms.

This project will build on technology developments at Strathclyde to demonstrate an integrated laser-cooled microwave atomic clock with state-of-the-art short term performance and long-term accuracy approaching that of an atomic fountain. The project therefore addresses a crucial scientific and technological challenge for delivering precise and stable timekeeping in a compact package that is scalable to mass manufacturing while matching or exceeding industry leading clock performance.