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Precision measurement in ultracold metastable helium atoms as a test of QED

February 5, 2015 - 10:30am
Ken Baldwin
The Australian National University

Helium is a favoured test bed for validating quantum electrodynamic theory through precision spectroscopic measurements.   We have previously measured transition rates in ultracold metastable helium atoms in order to test QED theory.  This includes the 23P1 and 23P2 transition rates to the ground state (measured for the first time), an upper bound on the 23P0 decay rate, and the metastable 23S1 state lifetime determined for only the second time with a five-fold improvement in accuracy.

More recently we have undertaken measurement of the tune out wavelength for metastable helium at which the atomic polarizability vanishes.  We utilise a novel, highly sensitive technique for precisely measuring the effect of variations in the trapping potential of magnetically confined atoms illuminated by a perturbing laser light field.  At a wavelength of 413.0878(9) nm we detect no change in the trapping potential for atoms output-coupled from the trap, which compares well with the value predicted by a theoretical calculation (413.02(9) nm) sensitive to non-relativistic quantum electro-dynamic effects, thereby providing motivation for more detailed theoretical investigations.


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