The fine-structure splitting in the $2{}^3{P}_J$ ($J=0$, 1, 2) levels of ${}^4\mathrm{He}$ is of great interest for tests of quantum electrodynamics and for the determination of the fine-structure constant $\alpha$. The $2{}^3{P}_0\text{−}2{}^3{P}_2$ and $2{}^3{P}_1\text{−}2{}^3{P}_2$ intervals are measured by laser spectroscopy of the ${}^3{P}_J\text{−}2{}^3{S}_1$ transitions at 1083 nm in an atomic beam, and are determined to be $31908130.98\pm 0.13\mathrm{kHz}$ and $2291177.56\pm 0.19\mathrm{kHz}$, respectively. Compared with calculations, which include terms up to ${\alpha }^5\mathrm{Ry}$, the deviation for the $\alpha$-sensitive interval $2{}^3{P}_0\text{−}2{}^3{P}_2$ is only 0.22 kHz. It opens the window for further improvement of theoretical predictions and an independent determination of the fine-structure constant $\alpha$ with a precision of $2\times {10}^{-9}$.

• Received 13 December 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.063001