Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius

Abstract

We measure the absolute frequency of seven out of the nine allowed transitions between the 2${}^3${\it S} and 2${}^3${\it P} hyperfine manifolds in a metastable ${}^3$He beam by using an optical frequency comb synthesizer-assisted spectrometer. The relative uncertainty of our measurements ranges from $1\times 10^{-11}$ to $5\times 10^{-12}$, which is, to our knowledge, the most precise result for any optical ${}^3$He transition to date. The resulting $2^3${\it P}-2${}^3${\it S} centroid frequency is $276702827204.8(2.4)$kHz. Comparing this value with the known result for the ${}^4$He centroid and performing {\em ab initio} QED calculations of the ${}^4$He-${}^3$He isotope shift, we extract the difference of the squared nuclear charge radii $\delta r^2$ of ${}^3$He and ${}^4$He. Our result for $\delta r^2=1.074(3)$ fm${}^2$ disagrees by about $4\sigma$ with the recent determination [R. van Rooij {\em et al.}, Science {\bf 333}, 196 (2011)].

4 pages, 3 figures, 3 tables

References in corpus (2)

• A high-precision variational approach to three- and four-nucleon bound and zero-energy scattering states
• Hyperfine Suppression of $2^3{\mathrm{S}}_1-3^3{\mathrm{P}}_J$ Transitions in ${}^3$He

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