Eur. Phys. J. D 57, 303-320 (2010)
https://doi.org/10.1140/epjd/e2010-00044-5

Ultra-sensitive magnetometry based on free precession of nuclear spins

¹ Institut für Physik, 55099 Mainz, Germany
² Physikalisch-Technische Bundesanstalt, 10587 Berlin, Germany
³ University of Virginia, Charlottesville, VA, 22904, USA

Corresponding author: wheil@uni-mainz.de

Received: 25 March 2009
Revised: 13 October 2009
Published online: 2 March 2010

Abstract

We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized ³He or ¹²⁹Xe samples with a SQUID as magnetic flux detector. The device will be employed to control fluctuating magnetic fields and gradients in a new experiment searching for a permanent electric dipole moment of the neutron. Furthermore, with the detection of the free precession of co-located ³He/¹²⁹Xe nuclear spins it can be used as ultra-sensitive probe for non-magnetic spin interactions, since the magnetic dipole interaction (Zeeman-term) drops out. Characteristic spin precession times T₂^* of up to 60 h were measured. The achieved signal-to-noise ratio of more than 5000:1 leads to an expected sensitivity level (Cramer-Rao lower bound) of δB≈1 fT after an integration time of 220 s and of δB≈10^-4 fT after one day. By means of a co-located ³He/¹²⁹Xe magnetometer, noise sources inherent in the magnetometer could be investigated, showing that CRLB is fulfilled, at least down to δB≈10^-2 fT. The reason for such a high sensitivity is that free precessing ³He (¹²⁹Xe) nuclear spins are almost completely decoupled from the environment. Therefore, this type of magnetometer is particularly attractive for precision field measurements where long-term stability is required.