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Accurately evaluating on 40Ca+ optical clock BBR temperature (Vol. 48 No. 2)

Modelled temperature distribution of the miniature Paul trap

Optical clock based on 40Ca+ single-ion is a promising option in the program of transportable optical clocks. In such system, one of the largest contributions to the systematic uncertainty is blackbody radiation (BBR) shift. The uncertainty of BBR shift is basically dependent on the uncertainty of the BBR shift coefficient and the uncertainty of temperature measurement on the trap environment which both have a contribution at 10-17 level in fractional frequency units. We report a careful evaluation of BBR temperature rise seen by 40Ca+ ion confined in a miniature Paul trap via FEM modelling. The result indicates that the uncertainty of the BBR shift due to temperature has a contribution of 5.4 × 10-18 to the systematic uncertainty, and it allows improving the clock’s overall accuracy in the future. Moreover, an interesting work has been reported on validating the finite-element temperature model by comparison with thermal camera measurements calibrated against PT1000 thermometers. This work can be used to validate the FEM model of other optical clock systems and to evaluate the temperature in a vacuum chamber measured by thermal camera.

P. Zhang, J. Cao, H. Shu, J. Yuan, J. Shang, K. Cui, S. Chao, S. Wang, D. Liu and X. Huang, Evaluation of blackbody radiation shift with temperature-associated fractional uncertainty at 10-18 level for 40Ca+ ion optical clock, J. Phys. B: At. Mol. Opt. Phys. 50, 015002 (2017).
[Abstract]