Description
The performance of optical atomic clocks has improved tremendously over the last two decades. The fractional frequency uncertainties of the best optical clocks reach the $10^{-18}$ level and currently outperform cesium fountain clocks, the current primary frequency standards defining the SI second, by two orders of magnitude. Redefinition of the SI second based on optical clocks is expected to take place in the next decade. The criteria require that optical clocks are evaluated with fractional frequency uncertainties of $3\times 10^{-18}$ or better, and compared with other devices in remote laboratories with uncertainties comparable to their evaluated uncertainties. In recent years, the frequency and time group at the National Research Council Canada (NRC) has been developing a high-accuracy transportable optical atomic clock for direct comparisons with clocks in other National Metrology Institutes.
The optical clock at NRC is based on the 445-THz $5s\,^{2}S_{1/2}\,$-$\,4d\,^{2}D_{5/2}$ electric quadrupole transition in $^{88}$Sr$^{+}$. The frequency reference is a single laser-cooled ion, suspended between two endcap electrodes with a radio-frequency (RF) electric field. An optical clock based on $^{88}$Sr$^{+}$ is well suited for the transportable system due to its simple energy-level structure, where only four lasers with easily accessible wavelengths are required for its operation. Furthermore, the systematic effects that perturb the clock transition are well understood, and can be controlled at or below the $10^{-18}$ level. Our transportable system is equipped with a newly-designed ion trap with improved thermal properties that is expected to reduce the blackbody radiation shift (BBRS) uncertainty by an order of magnitude compared to our existing stationary clock. It also has a compact vacuum chamber with 10 times lower background gas pressure, which is expected to reduce the collisional frequency shift (CFS) by the same factor.
With these upgrades, all the systematic effects in the transportable system are expected to be below the $10^{-18}$ level. For further improved performance, we have recently started to build a cryogenic $^{88}$Sr$^{+}$ optical clock, where both the BBRS and CFS will be suppressed below the $10^{-19}$ level. Future comparisons between cryogenic and transportable clocks will validate the accuracy of our ensemble of $^{88}$Sr$^{+}$ clocks.
We will present a brief overview of our $^{88}$Sr$^{+}$ clock system, and the current status and future prospects of both the transportable and cryogenic systems.
| Presenter name | Kosuke Kato |
|---|---|
| How will you attend ICAP-27? | I am planning on in-person attendance |
