Description
At the National Research Council Canada (NRC), an optical frequency standard based on a single trapped strontium ion has been developed. The optical clock uses the 5s $^2S_{1/2}$ – 4d $^2D_{5/2}$ electric quadrupole transition of the $^{88}\mathrm{Sr}^+$ ion at 445 THz as its reference transition. This clock transition of the $^{88}\mathrm{Sr}^+$ ion has been recommended as one of the secondary representations of the SI second. Currently, the overall systematic uncertainty of NRC’s $^{88}\mathrm{Sr}^+$ ion clock is $1.2\times10^{-17}$ in fractional frequency units, which is mainly limited by the blackbody radiation (BBR) shift uncertainty of $1.1\times10^{-17}$.
The BBR shift is caused by the interaction of the energy levels of the clock transition with the electric field of the thermal radiation at the ion position. The BBR shift uncertainty of our $^{88}\mathrm{Sr}^+$ ion clock is mainly limited by the evaluation of the electric field caused by the thermal radiation. The other two parameters needed to determine the BBR shift, namely the polarizability and the dynamic correction of the clock transition, can either be measured or calculated accurately and their contributions to the uncertainty of the BBR shift is below $10^{-18}$.
In order to evaluate the thermal electric field experienced by the $^{88}\mathrm{Sr}^+$ ion in the optical frequency standard, we built a copy of ion trap and installed it in an offline vacuum chamber dedicated to thermal imaging measurements. A calibrated IR camera has been used to measure the temperature change of the test trap components when a drive rf voltage is applied to electrodes. To increase the accuracy of the temperature measurements using the IR camera, key trap components were painted with matte black paint to increase emissivities. The temperature data of the test trap components will be compared to a finite element simulation from which the effective thermal electric field experienced by the $^{88}\mathrm{Sr}^+$ ion can be extracted for the evaluation of the BBR shift and its uncertainty.
It is expected that the overall uncertainty of the $^{88}\mathrm{Sr}^+$ ion optical clock will be reduced to the $\sim5\times10^{-18}$ level with the results of the current study.
| Presenter name | Bin Jian |
|---|---|
| How will you attend ICAP-27? | I am planning on in-person attendance |
