Experimental classification of multi-spin coherence under the full rotation group

Abstract

The density operator of a coupled nuclear spin system often includes multi-spin coherences representing correlations between different spins. The generation and evolution of these coherences is governed by the dipole-dipole interactions between the spins and thus contains information about nuclear structure. Different multi-spin coherences may be distinguished by their behaviour under rotations. The maximum information extractable is determined by the irreducible representations of the full rotation group SO (3). By comparing the effect of rotation with various angles and rotation axes one can determine the expansion coefficients of the spin density operator in a basis of irreducible tensor operators. Experimentally, the rotation of the spins is achieved with rf pulses.