Robust conversion of singlet spin order in coupled spin-1/2 pairs by   adiabatically switched RF-fields
  We propose a robust and highly efficient NMR technique to create singlet spin order from longitudinal spin magnetization in coupled spin-1/2 pairs and to perform backward conversion (singlet order)$\to$magnetization. In this method we exploit adiabatic switching of an RF-field in order to drive transitions between the singlet state and the $T_\pm$ triplet states of a spin pair under study. We demonstrate that the method works perfectly for both strongly and weakly coupled spin pairs, providing a conversion efficiency between the singlet spin order and magnetization, which is equal to the theoretical maximum. We anticipate that the proposed technique is useful for generating long-lived singlet order, for preserving spin hyperpolarization and for assessing singlet spin order in nearly equivalent spin pairs in specially designed molecules and in low-field NMR studies. 
Andrey N. Pravdivtsev, Alexey S. Kiryutin, Alexandra V. Yurkovskaya,   Hans-Martin Vieth, Konstantin L. Ivanov
physics.chem-ph cond-mat.mes-hall