Macroscopic hyperpolarization enhanced with quantum optimal control

Hyperpolarization of nuclear spins enhances nuclear magnetic resonance signals, which play a key role for imaging and spectroscopy in the natural and life sciences. This signal amplification unlocks previously inaccessible techniques, such as metabolic imaging of cancer cells. In this paper, electron spins from the photoexcited triplet state of pentacene-doped naphthalene crystals are used to polarize surrounding protons. As existing strategies are rendered less effective by experimental constraints, they are replaced with optimal control pulses designed with redcrab. In contrast to previous optimal control approaches, which consider one or two effective nuclei, this closed-loop optimization is macroscopic. A 26% improvement in signal and 15% faster polarization rate are observed. Additionally, a strategy called autonomously optimized repeated linear sweep (ARISE) is introduced to efficiently tailor existing hyperpolarization sequences in the presence of experimental uncertainty to enhance their performance. ARISE is expected to be broadly applicable in many experimental settings.