Coherent Population Trapping (CPT) clocks

Some embedded applications require a self-contained absolute time/frequency reference that can only be provided by an atomic clock. These applications require modest performance atomic clocks of course, but with a high miniaturization degree associated with very low power consumption and high reliability. The long-term goal is to install them in GNSS receivers, professional mobile phones, etc.

A promising concept of an atomic clock meeting these needs is based on the Coherent Population Trapping (CPT) phenomenon. This is a quantum phenomenon different from that encountered in vapor cell rubidium clocks, but which also allows to perform simultaneously the main interactions with only two laser beams: state preparation, atoms interrogation and absorption clock signal detection.

The great advantage of the CPT technique is to get rid of the microwave resonant cavity, which allows greater miniaturization of the clock physical part and its mass production easier by microfabrication techniques. The ultimate goal is to realize centimetric CPT clocks. Already very compact industrial devices (< 17 cm3, consumption < 120 mW) are on the market and compete with traditional vapor cell rubidium clocks on part of the market.

Tracks for improving CPT clocks are on the one hand the pursuit of miniaturization and the power consumption reduction, on the other hand the improvement of performance, for example by using a pulsed interrogation technique similar to that proposed by N. Ramsey.

CPT industrial clock (source: Microsemi)
CPT clock microcell developed at FEMTO-ST