Laser spectroscopic determination of the $^{6}$He nuclear charge radius*

The weakly bound $^{6}$He nucleus is an excellent testing ground for few-body nuclear calculations and is of great interest since its halo structure was suggested in the 80s. In this thesis work, we performed precision laser spectroscopy on individual metastable $^{6}$He atoms confined and cooled in a magneto-optical trap (MOT). This technique enabled us to accurately measure the isotope shift between $^{6}$He and $^{4}$He to be 43194.772(56) MHz in the 2$^{3}$S$_{1}$--3$^{3}$P$_{2}$ transition at 389 nm. Based on this measurement and the atomic theory calculation, the root-mean-square charge radius of $^{6}$He was determined to be 2.054(14) fm [1]. This result confirmed the neutron-halo structure of the $^{6}$He nucleus model-independently for the first time and helps reveal the structure of the loosely bound system. This experiment also demonstrates a new technique for precision laser spectroscopy of short-lived radioactive atoms, and provides a unique atomic method for nuclear physics studies. [1] L.-B. Wang \textit{et al}., Phys. Rev. Lett. \textbf{93}, 142501 (2004)