Numerical analysis of relaxation times of multiple quantum coherences in the system with a large number of spins

TL;DR

This paper analyzes how multiple quantum NMR coherences decay in large spin systems, showing that relaxation times decrease with coherence order and number of spins, and explores effects of perturbations on decoherence.

Contribution

It introduces a detailed analysis of MQ NMR coherence decay in large spin systems and examines the impact of perturbations on decoherence rates.

Findings

Relaxation time decreases with increasing MQ coherence order.

Relaxation time decreases as the number of spins increases.

Perturbations influence the decoherence rate in large spin systems.

Abstract

We study the decay of multiple quantum (MQ) NMR coherences in systems with the large number of equivalent spins. As being created on the preparation period of MQ NMR experiment, they decay due to the dipole-dipole interactions (DDI) on the evolution period of this experiment. It is shown that the relaxation time decreases with the increase in MQ coherence order {(according to the known results)} and in the number of spins. We also consider the modified preparation period of MQ NMR experiment (G.A.Alvarez, D.Suter, PRL {\bf 104}, 230403 (2010)) concatenating the short evolution periods under the secular DDI Hamiltonian (the perturbation) with the evolution period under the non-secular averaged two-spin/two-quantum Hamiltonian. The influence of the perturbation on the decoherence rate is investigated for the systems consisting of 200-600 equivalent spins.