Optically detected nuclear magnetic resonance of coherent spins in a molecular complex.

Nuclear magnetic resonance is a powerful tool for applications ranging from chemical analysis to quantum information processing. Achieving optical initialization and detection of molecular nuclear spins promises new opportunities-including improved nuclear magnetic resonance signals at low magnetic field, sensitivity down to the single-molecule level and full access to atomically precise molecular architectures for quantum technologies. Here we report the optical read-out of coherently controlled nuclear spins in a europium-based molecular crystal. By harnessing ultranarrow optical transitions, we achieve the optical initialization and detection of nuclear spin states. Through radio-frequency driving, we address two nuclear quadrupole resonances, characterized by narrow inhomogeneous linewidths and a distinct correlation with the optical transition frequency. We implement Rabi oscillations, spin echo and dynamical decoupling techniques, achieving nuclear spin quantum coherence with a lifetime of up to 2 ms. These results highlight the capabilities of optically detected nuclear magnetic resonance and underscore the promise of molecular nuclear spins for quantum information processing.