Separated-oscillatory-field measurement of the n=10F3+−+G4interval in helium: A 200-part-per-billion measurement

Abstract

The n=10 {sup +}F{sub 3}-{sup +}G{sub 4} energy interval in helium is measured to an accuracy of 200 parts per billion. Rydberg states of helium are created by charge exchange between a helium ion beam of a few keV and a dense thermal beam of neutral cesium atoms. A microwave transition is driven between the two states in a Ramsey-separated-oscillatory-field configuration yielding a linewidth of less than 0.2 MHz. The result of 2017.3254(4) MHz is the most accurate measurement of any Rydberg fine structure and can be compared to a similarly accurate theoretical prediction of this interval. This comparison gives a very high-precision test of physics on the large-distance scale of these Rydberg states, including the nonrelativistic Coulomb potential, relativistic effects, and quantum-electrodynamical effects such as the retardation (or Casimir) interactions. A disagreement between theory and experiment indicates the possibility of additional new physics on this distance scale. {copyright} {ital 1997} {ital The American Physical Society}