Fig. 2.

Coherent hyperpolarization experiments. a DARTH_SABRE pulse sequence, where DARTH-pulses of length τ_p are given at intervals of τ_d for “n” repetitions and applied to the bound ¹⁵N spin slightly off-resonance. The pulses adiabatically ramp towards the optimal matching condition to induce higher polarizations. b Coherent SHEATH pulse sequence, where analogous pulses are delivered to the sample at the optimal field condition, which is typically ≈0.5 μT, with inter-pulse delays using a ≈55 μT field to store magnetization. c Experimental DARTH-SABRE dynamics of an AA’XX’ spin system using 50 mM ¹⁵N-pyridine with an inter-pulse delay of τ_d=600 μs at 8.45 T. d Experimental coherent SHEATH dynamics of an AA’X spin system using 100 mM ¹⁵N-benzonitrile with 33 mM pyridine and an inter-pulse delay of τ_d = 350 ms; detection was performed at 8.45 T. Data are shown fit to numerical QMC simulations using average PTC lifetimes of 20 ms (DARTH) and 50 ms (SHEATH). e Polarization as a function of the delay parameter for the DARTH-SABRE sequence using a 25 ms DARTH pulse, which corresponds to a π pulse. f Evolution of singlet population excess (DARTH AA’XX’: S_H⁰–T_H⁰, blue line; SHEATH AA’X: S_H⁰–T_H^-, red line) under the conditions used in the fit of the experimental data and normalized to the initial S_H⁰ population