Speaker
Description
Paving the way for bound-state QED tests in singly ionized helium
Authors: J.J. Krauth, L.S. Dreissen, C. Roth, E.L. Grundeman, M. Favier,
M. Collombon, K.S.E. Eikema
Affiliation: LaserLaB, Vrije Universiteit Amsterdam, The Netherlands
Abstract:
For several decades bound-state quantum electrodynamics has been tested
successfully by laser spectroscopy experiments on hydrogen. These
measurements nowadays reach a relative precision of down to $10^{-15}$.
At this level of precision the value of the proton radius, as well as
difficult-to-evaluate higher-order 2-loop QED terms play an essential
role and limit future improvements. About 10 years ago the CREMA
collaboration has measured the proton radius in muonic hydrogen and
shook the community with a result which is in strong disagreement with
the current CODATA value. The CODATA value combines several measurements
with electronic hydrogen. Many atomic physics research groups are
currently working towards understanding this puzzle.
We are developing the next generation of bound-state QED tests based on
high precision measurements in singly ionized helium. We aim to measure
the 1S-2S transition frequency in the extreme ultra-violet of a single
trapped He$^+$ ion to an accuracy of below 1\,kHz. Due to the twofold
nuclear charge, this measurement is very sensitive to the above
mentioned QED terms. In combination with nuclear charge radius
experiments conducted in muonic helium ions our results will set a
benchmark for future QED calculations or can be used as a crosscheck
concerning the proton radius puzzle.
We will measure the 1S-2S transition using the Ramsey-Comb Spectroscopy
(RCS) method. RCS uses two amplified and upconverted pulses from the
pulse train of a frequency comb laser to perform a Ramsey-like
excitation. In this talk I will give an overview of the experiment and
present recent results from measurements on xenon where we use pulse
pairs upconverted to 110\,nm by high-harmonic generation (HHG). With
these measurements we reach an accuracy of below 1\,MHz, which is
unprecedented with a light source from HHG. The HHG will later be
extended to the XUV range, in order to create light at a wavelength of
32\,nm for the measurement in He$^+$.