Magic composite pulses

TL;DR

This paper introduces composite pulses that control dipolar interactions in spin ensembles, improving the robustness of NMR sequences against experimental imperfections using geometric and average Hamiltonian theory.

Contribution

It presents a novel construction method for composite pulses based on average Hamiltonian theory and geometrical properties, enhancing the magic sandwich sequence in NMR.

Findings

Magic composite pulses improve the magic sandwich effect.

Numerical simulations confirm robustness against experimental defects.

Magic composite pulses outperform standard b1/2 pulses in NMR sequences.

Abstract

I describe composite pulses during which the average dipolar interactions within a spin ensemble are controlled while realizing a global rotation. The construction method used is based on the average Hamiltonian theory and rely on the geometrical properties of the spin-spin dipolar interaction only. I present several such composite pulses robust against standard experimental defects in NRM: static or radio-frequency field miscalibration, fields inhomogeneities. Numerical simulations show that the magic sandwich pulse sequence, a pulse sequence that reverse the average dipolar field while applied, is plagued by defects originating from its short initial and final \pi/2 radio-frequency pulses. Using the magic composite pulses instead of \pi/2 pulses improves the magic sandwich effect. A numerical test using a classical description of NMR allows to check the validity of the magic composite pulses and estimate their efficiency.