Multi-spin control from one-spin pulses

TL;DR

This paper introduces a new method for controlling weakly coupled spin systems using single-spin optimized RF pulses, simplifying the process and avoiding complex multispin optimizations.

Contribution

The authors develop a framework that creates multi-spin control pulses from single-spin optimizations, enabling efficient and robust control of weakly coupled spins without multispin optimization.

Findings

Successfully designed band-schematic pulses for selective spin transfer.

Implemented a joint INEPT sequence achieving band-selective transfer.

Framework allows rapid pulse generation and analysis in software Seedless.

Abstract

Controlling ensembles of weakly coupled spins typically requires computationally expensive multispin optimisations. We present a compact framework that enables control of weakly coupled spin systems (of any spin), but using RF pulses optimised for a single spin-1/2. We do this by explicitly creating a GRAPE pulse with fixed 'active' evolution times using single spin-1/2 methods, and pulsing on one spin at a time. By enforcing this form uniformly across offsets ('band-schematic' pulses),chemical shift and scalar coupling evolution of the entire system can be precisely controlled. We demonstrate the approach by constructing band-schematic pulses and a continuously irradiated joint INEPT (JINEPT) that achieves band-selective transfer $I_z \rightarrow 2I_zS_z$. The framework is implemented in the software Seedless, which both rapidly generates such pulses and analyses the schematic form of arbitrary pulses, enabling robust multi-spin control, without multi-spin optimisation.