Finite element analysis of blackbody radiation environment for an ytterbium lattice clock operated at room temperature

Abstract

The Stark shift due to blackbody radiation (BBR) is a key obstacle limiting the frequency uncertainty of optical lattice clocks. A well-characterized BBR environment is necessary to know exactly the temperature felt by the cold atoms. In our ytterbium clock, the lattice-trapped atoms are exposed to the thermal radiation of the surrounding vacuum chamber walls and optical windows. Calibrated platinum resistance temperature detectors are used to monitor the vacuum chamber temperature in real time. In order to obtain the effective temperature T eff in the position of the atoms, we perform finite element (FE) analysis to the thermal radiation of the vacuum chamber. Due to the temperature inhomogeneity existing in our vacuum chamber, the limited knowledge of the air convection contributes the largest part of the uncertainty in T eff. For our typical room temperature environment, T eff can be determined with an accuracy level of 160 mK, corresponding to a fractional frequency uncertainty of 5.3 × 10−18 for the BBR Stark shift. Additionally, we use a simple formula to relate T eff to the temperatures at the monitored points, which allows us to know the value of T eff without using FE analysis, and thus enables the real-time correction to the BBR Stark shift.