Direct measurement of the 3He+ magnetic moments

Helium-3 has nowadays become one of the most important candidates for studies in fundamental physics(1-3), nuclear and atomic structure(4,5), magnetometry and metrology(6), as well as chemistry and medicine(7,8). In particular, He-3 nuclear magnetic resonance (NMR) probes have been proposed as a new standard for absolute magnetometry(6,)(9). This requires a high-accuracy value for the He-3 nuclear magnetic moment, which, however, has so far been determined only indirectly and with a relative precision of 12 parts per billon(10,)(11). Here we investigate the He-3(+) ground-state hyperfine structure in a Penning trap to directly measure the nuclearg-factor of He-3(+) g(I)' = -4.2550996069(30)(stat)(17)(sys), the zero-field hyperfine splitting E-HFS(exp) = -8,665,649,865.77(26)(stat) (1)(sys )Hz and the bound electrong-factor g(e)(exp) = -2.00217741579(34)(stat)(30)(sys). The latter is consistent with our theoretical value g(e)(theo) = - 2.00217741625223(39) based on parameters and fundamental constants from ref.(12). Our measured value for the He-3(+) nuclearg-factor enables determination of the g-factor of the bare nucleus g(I) = -4 .255250 6997 (30)(stat)(17)(sys)(1)(theo) via our accurate calculation of the diamagnetic shielding constant(13 )sigma(3)(He+) = 0.00003550738(3). This constitutes a direct calibration for He-3 NMR probes and an improvement of the precision by one order of magnitude compared to previous indirect results. The measured zero-field hyperfine splitting improves the precision by two orders of magnitude compared to the previous most precise value(14) and enables us to determine the Zemach radius (15)to r(Z) = 2.608(24) fm.

Automated summary

Helium-3 has become a significant candidate for research in various fields. In this study, the nuclear magnetic moment and hyperfine structure of He-3(+) were directly measured, providing a direct calibration for He-3 NMR probes and improving the precision of magnetometry by one order of magnitude. The measured values also enabled the determination of the Zemach radius with higher precision compared to previous results.