Hyperpolarized multiple quantum coherences at ultra-low magnetic fields increase 15N parahydrogen-induced polarization

We used signal amplification by reversible exchange of parahydrogen (SABRE) at low (~1 mT) and ultra-low (~1 μT, ULF) magnetic fields. We proposed and used ULF correlation spectroscopy (COSY) method to analyze PHIP spin order in real-time. Coherences up to the third-order were observed experimentally. Furthermore, we analyzed SABRE in alternating magnetic fields (alt-SABRE). We measured the evolution of 1H-15N zero-quantum coherences and have shown that they persist during field alternation and depend on the magnetic field strength. The resulting 15N-polarization in the alt-SABRE experiment was with magnetic was appoximately 30% higher