Departmental Seminar

Precision Measurement of the Helium 23S1 – 23P/33P Tune-Out Frequency as a Test of QED

Mr Bryce Henson
Dept of Quantum Science and Technology

 Advancements in atomic physics have been continually driven by the interplay of experimental measurement and theoretical prediction, each offering a challenge to the other as precision improves. Recently, as the precision of atomic spectroscopy approaches the part-per-trillion level discrepancies between predictions and experiments have come to light. For example, the `proton radius puzzle' wherein spectroscopic measurements yield determinations of the proton radius which disagree by up to five standard deviations with other approaches. To shed new light on this disagreement we break the modus operandi of experimental spectroscopy which measures differences in atomic energy levels, and focus on transition strengths, which have remained poorly constrained experimentally. 

In this talk I will present our precision measurement of a tune-out frequency in metastable helium as a high precision test of theoretically predicted transition strengths. The tune-out allows this test by sidestepping limitations of direct transition strength measurements and instead measures the balance point of multiple transitions. I will describe the novel theoretical and experimental methods that have enabled this measurement, such as measuring trap frequency using a pulsed atom laser and sensing optical potentials as small as 10–35 J. I will discuss the findings of this research and discuss new directions for research in the He* BEC lab with helium-3.

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