J-PARC素粒子原子核セミナー（Dr. Andreas Mooser）
Recent advances in quantum-jump spectroscopy of single isolated nucleons in a Penning trap led to most precise measurements of the nuclear magnetic moments of the proton [1, 2] and its antimatter counterpart . Based upon these successes a new experiment dedicated to the measurement of the nuclear magnetic moment of ^3He^2+, μHe, is being set up at the Max-Planck-Institute for nuclear physics in Heidelberg (Germany) in collaboration with RIKEN and the University of Mainz. The project aims at the first direct measurement of μHe with a relative precision of 10^−9 or better.
The measurement of μHe will complement hyper-polarized 3He as an independent magnetometer, which potentiality exhibits small systematic corrections concerning sample shape, impurities and environmental dependencies. Making use of optical pumping and long relaxation times in low-pressure 3He gas cells, relative precisions of 10^−12 within seconds were already achieved . However so far, the 3He probes do not provide an absolute calibration independent of H2O, be- cause the magnetic moment of 3He was only determined by measuring the 3He NMR frequency relative to the NMR frequency of H2O . This limitation can be overcome by the planned direct measurement of μHe.
Once μHe is measured independent from H2O probes, hyper-polarized 3He can serve as an uncorrelated magnetic field probe with very different and in cases smaller systematic effects compared to H2O probes. Thus it has the potential to second challenging absolute magnetic field measurements using H2O with an additional probe as e.g. in the case of the planned g − 2 measurement of the muon. In addition, a complementary determination of the anomalous magnetic moment of the muon becomes possible.
To date, direct high-precision measurements of nuclear magnetic moments of single ions in a Penning trap have been demonstrated only for the proton and the antiproton. The employed methods rely on the detection of single spin flips whose detection fidelity is however limited by the energies of the trapped ions . If applied to μHe, the methods would hinge upon an insufficient detection fidelity. Thus, to meet the challenge of the high-fidelity spin-flip detection, the experiment aims to decrease the energy by more than two orders of magnitude compared to classical approaches [1, 2, 3]. This will be achieved by applying sympathetic laser cooling, coupling a single 3He ion to a reservoir of laser-cooled beryllium ions . From this quasi-deterministic cooling scheme a considerable reduction in experimental cycle times and a high-fidelity spin state detection are expected.
In the talk prospects of an absolute magnetic field probe using 3He, developments towards sympathetic laser cooling and the developments towards the μHe measurement will be presented.
 A. Mooser et al., Nature 509, 596 (2014).  G. Schneider et al., Science 358, 1081 (2017).  C. Smorra et al., Nature 550, 371 (2017).  A. Nikiel et al., Eur. Phys. J. D 68, 330 (2014).  J. Flowers et al., Metrologia 30, 75 (1993).  A. Mooser et al., Phys. Rev. Lett. 110, 140405 (2013).  M. Bohmann, J. Mod. Opt. 65, 568 (2017).