Effects of an arbitrarily oriented rotating field in magnetic resonance

L. N. Novikov, S. L. Votyakov, V. P. Suetin

M. Allegrini, E. Arimondo

David Thomas Pegg

The magnetic resonance of a spin-half system in a static field and an arbitrarily oriented oscillating field has been studied recently by McClean and Swain (1976) by a continued-fraction technique in quantum-electrodynamical perturbation theory, a difficult procedure involving twenty fourth-order processes and some rather heavy analysis. It is shown how the semiclassical approach of Pegg and Series (1970, 1973) yields the same results more simply. This approach also has the advantage of being applicable to systems of arbitrary spin.

Stuart J. Ingleby, Erling Riis, Aidan S. Arnold +3 more

Our magnetometry development is focussed on compact, portable sensors for geophysical field measurements. In order to develop practical sensors with minimised size and power requirements, single-beam double-resonance magnetometry is used, avoiding any requirement for extensive optical hardware or full-field compensation. Magnetic resonance in atomic polarisation is detected using a polarimeter to measure optical rotation in transmitted pump light, allowing rejection of common-mode optical noise. The application of this technique to unshielded geophysical field measurements requires detailed understanding of systematic effects arising in arbitrary orientations of the static field B0. We report the development and calibration of a test system for double resonance measurements in generated static fields of well-controlled magnitude and orientation, including systems for automated B0 control and software generated modulation/demodulation [1]. The sensitivity of these devices depends on signal amplitude, phase and RF broadening, all of which vary with B0 orientation. By working in a low-field, weak-pumping regime, we obtain experimental measurements of anisotropy in these parameters, in agreement with theoretically derived distributions [2]. We comment on the importance of measurement mode and signal demodulation in optimising double-resonance sensitivity and bandwidth, and the suitability of these techniques for compact, portable magnetometers. This work is supported by the UK Quantum Technology Hub in Sensors and Metrology [3].

Alexandre Faribault, Hugo Tschirhart

In this work we demonstrate a simple way to implement the quantum inverse scattering method to find eigenstates of spin-1/2 XXX Gaudin magnets in an arbitrarily oriented magnetic field. The procedure differs vastly from the most natural approach which would be to simply orient the spin quantisation axis in the same direction as the magnetic field through an appropriate rotation. Instead, we define a modified realisation of the rational Gaudin algebra and use the quantum inverse scattering method which allows us, within a slightly modified implementation, to build an algebraic Bethe ansatz using the same unrotated reference state (pseudovacuum) for any external field. This common framework allows us to easily write determinant expressions for certain scalar products which would be highly non-trivial in the rotated system approach.

Е. А. Иванченко