Preparation Efficiency of Singlet States in Multi-spin Systems with Different Coupling Configurations

Abstract

Nuclear spin singlet is a special quantum state that lasts longer than T1 and can be used to study slow diffusion and motion between molecules. The preparation of singlet states is the key to their successful application. Currently, various methods for preparing singlet states have been reported in the literature, which are mainly applicable to isolated two-spin systems. When the nuclear spin involved in the singlet state is coupled to other spins, the preparation efficiency of the singlet state often decreases. In this paper, taking a three-spin system as an example, we studied the effect of non-singlet spin coupling on the preparation efficiency of singlet states under different coupling configurations. The simulation results show that as the singlet spin changes from weak coupling to strong coupling, the preparation efficiency of the singlet state will maintain a certain stability when the coupling between the singlet spin and the non-singlet spin is symmetrical. This characteristic can provide a reference for selecting appropriate spins to prepare singlet states in complex systems. We experimentally verified this conclusion using a three-spin system in the N-acetyl-L-aspartic acid (NAA) molecule. By adjusting the pH of the NAA molecule, the three-spin system can transfer from weak coupling to strong coupling. The experimental results show that the preparation efficiency of the singlet state is significantly higher when the three spins are in strong coupling than that when the spins are in weak coupling.

Keywords

• nmr
• nuclear spin singlet state
• preparation efficiency
• naa
• pulse sequence
• optimal control