Ultra-sensitive magnetometry based on free precession of nuclear spins

TL;DR

This paper presents a highly sensitive low-field magnetometer using free nuclear spin precession of 3He or 129Xe, achieving femtotesla sensitivity suitable for precision magnetic field measurements and fundamental physics experiments.

Contribution

It introduces a novel magnetometry technique based on free nuclear precession with unprecedented sensitivity and long spin coherence times, enabling new precision measurement applications.

Findings

Achieved sensitivity of 1fT after 220s integration

Measured spin precession times up to 60 hours

Performance limited by statistical noise, not device noise

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 as well as in a new type of 3He/129Xe clock comparison experiment which should be sensitive to a sidereal variation of the relative spin precession frequency. Characteristic spin precession times T_2 of up to 60h could be measured. In combination with a signal-to-noise ratio of > 5000:1, this leads to a sensitivity level of deltaB= 1fT after an integration time of 220s and to deltaB= 10^(-4)fT after one day. Even in that sensitivity range, the magnetometer performance is statistically limited, and noise sources inherent to the magnetometer are not limiting. The reason is that free precessing 3He (129Xe) nuclear spins are almost completely decoupled from the environment. That makes this type of magnetometer in particular attractive for precision field measurements where a long-term stability is required.