Decoupling dipolar interactions in dense spin ensembles

Abstract

Dense spin ensembles in solids present a natural platform for studying quantum many-body dynamics. Multiple-pulse coherent control can be used to manipulate the magnetic dipolar interaction between the spins to engineer their dynamics. Here, we investigate the performance of a series of well-known pulse sequences that aim to suppress interspin dipolar couplings. We use a combination of numerical simulations and solid-state nuclear magnetic resonance experiments on adamantane to evaluate and compare sequence performance. We study the role of sequence parameters like interpulse delays and resonance offsets. Disagreements between experiments and theory are typically explained by the presence of control errors and experimental nonidealities. The simulations allow us to explore the influence of factors such as finite pulse widths, rotation errors, and phase transient errors. We also investigate the role of local disorder and establish that it is, perhaps unsurprisingly, a distinguishing factor in the decoupling efficiency of spectroscopic sequences (that preserve Hamiltonian terms proportional to S_{z}) and time-suspension sequences (which refocus all terms in the internal Hamiltonian). We discuss our findings in the context of previously known analytical results from average Hamiltonian theory. Finally, we explore the ability of time-suspension sequences to protect multispin correlations in the system.