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 [3]. 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 [4]. 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 [5]. 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 [6]. 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 [7]. 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.
[1] A. Mooser et al., Nature 509, 596 (2014).
[2] G. Schneider et al., Science 358, 1081 (2017).
[3] C. Smorra et al., Nature 550, 371 (2017).
[4] A. Nikiel et al., Eur. Phys. J. D 68, 330 (2014).
[5] J. Flowers et al., Metrologia 30, 75 (1993).
[6] A. Mooser et al., Phys. Rev. Lett. 110, 140405 (2013).
[7] M. Bohmann, J. Mod. Opt. 65, 568 (2017).