Keeping atoms synchronized for better timekeeping

Atomic clocks often have a limited coherence time due to the interactions between the constituent atoms. While it is usually very easy to use fewer atoms to reduce the interactions, this leads to lower signal-to-noise and less precise measurements. This tension between strong interactions and noise seems unavoidable and limits the accuracy of the world’s best cesium clocks, the keepers of international atomic time [1, 2]. As reported in a paper in Physical Review Letters, Christian Deutsch and coworkers at three laboratories in Paris, France, have circumvented this seemingly unavoidable compromise by showing that a clock’s coherence can actually be enhanced by strong atomic interactions [3]. Even better, strong atomic interactions might also reduce the clock’s systematic frequency shifts. The authors demonstrated long coherence times with an “atom chip,” but their key requirements can also be satisfied in optical lattice clocks [4].