Measuring the n=2 triplet P fine structure of atomic helium using frequency-offset separated oscillatory fields

The n=2 triplet P fine structure of atomic helium is being measured using microwave transitions.

The method [1] of Frequency-Offset Separated Oscillatory Fields (FOSOF) is used to perform

the measurements. The measurement of the J=1-to-J=2 interval has been completed [2], with a

measurement uncertainty of only 25 Hz. The measurement of the 29.6-GHz J=0-to-J=1 interval

is nearing completion. These measurements, together with sufficiently precise theoretical

predictions for the intervals (see [3] for the current state-of-the-art calculations) can be used to

determine a value for the fine-structure constant and to test for possible physics beyond the

standard model.

[1] A. C. Vutha and E. A. Hessels, Phys. Rev. A 92, 052504 (2015).

[2] K. Kato, T. D. G. Skinner and E. A. Hessels, Phys. Rev. Lett. 121, 143002 (2018).

[3] K. Pachucki and V. A. Yerokhin, Phys. Rev. Lett. 104, 070403 (2010).