Precision spectroscopy of the 2S-6P transition in atomic hydrogen and deuterium

Both atomic hydrogen and deuterium can be used to determine physical constants and to test bound-state quantum electrodynamics (QED) to very high precision. By combining at least two transition frequency measurements in each isotope, the proton and deuteron radius, along with the Rydberg constant, can be determined independently [1]. This is particularly interesting because, while recent hydrogen measurements [2] have agreed with the results from muonic hydrogen, no recent deuterium measurements are available and a discrepancy with muonic deuterium persists [3].

We recently measured the 2S-6P transition in hydrogen with a relative uncertainty below one part in 10¹², allowing one of the most stringent tests of bound-state QED. Here, we report on the status of the ongoing analysis. We also performed a preliminary measurement of the same transition in deuterium. The measurement in deuterium is complicated by the simultaneous excitation of hyperfine transitions, which can lead to unresolved quantum interference [4]. We have studied such effects, along with others, in detail, and conclude that a 2S-6P deuterium measurement with similar precision as for hydrogen is feasible.