We report a high-accuracy direct measurement of the blackbody radiation shift (BBR) of 133Cs ground state hyperfine transition. This frequency shift is one of the largest systematic frequency biases encountered in realizing the current definition of the SI second. Uncertainty in the correction of the BBR frequency shift has led to its being the focus of intense theoretical effort by a variety of research groups. Our experimental measurement of the shift used two laser-cooled primary frequency standards operating at different temperatures. We achieved an uncertainty a factor of five smaller than the previous best direct measurement. These results tend to validate the claimed accuracy of the recently calculated values.
Citation: Physical Review Letters
Pub Type: Journals
Blackbody Radiation, Cesium Clock, Primary Frequency Standard