There is a worldwide need for clocks with relative frequency uncertainties lower than 10-16 e.g. in metrology, basic science, geodesy, navigation and environmental monitoring. Such uncertainties can only be achieved by optical atomic clocks. The caesium atomic clocks currently used as the primary realisations of the SI second lag behind in precision by an order of magnitude. It is expected that the development of optical atomic clocks will lead to a new definition of the second in the SI unit system.
We at VTT MIKES are carrying out research on strontium single-ion optical clocks. When operating such a clock, a neutral atom from an atomic beam is first photo-ionised and captured in a radiofrequency trap. The captured ion is then laser cooled down to less than one millikelvin, after which a clock laser probes the reference transition and a frequency comb counts the oscillations of the clock laser.
Recently, we have operated for the first time the ion clock for several weeks. We found that the clock stability was limited by the magnetic-field noise from the Helsinki-Espoo metro, whereas the uncertainty was limited by variations in the ambient temperature. Preliminary measurements with the new mu-metal magnetic shields showed to improve the stability by more than an order of magnitude. A first evaluation of the uncertainty budget is ongoing. A total relative systematic uncertainty of a few parts in 10–18 is expected. Further improvements in the setup, e.g. in temperature control, are expected to help us reach our long-term goal: relative uncertainty below 10–18. Ion storage times of more than six weeks motivate developing new routines for operating the clock automatically for extended periods.
Please watch a video on the clock with new magnetic shields.
We also warmly recommend you to listen to the episode on atomic clocks in the popular science radio program Tiedeykkönen in Yle Areena, in which our Senior Scientist Anders Wallin is interviewed: “Atomikellot tikittävät tarkkaa aikaa – pörssi, sähköverkot ja satelliittipaikantaminen tarvitsevat sitä”.
New design for the ion trap.