Enhancing spin coherence of an optically addressed molecular qubit by nuclear spin hyperpolarization

Optically addressable molecular triplet spins provide a chemically tunable platform for quantum applications, but their coherence is typically limited by interactions with the surrounding nuclear spin bath. Here we demonstrate controlled suppression of nuclear-bath-induced decoherence via hyperpolarization of the nuclear spin bath through dynamic nuclear polarization (DNP). This approach is demonstrated in an optically addressable triplet molecular qubit system based on pentacene, where the achieved high proton polarization reduces magnetic noise from nuclear spin fluctuations and enhances the triplet spin transverse coherence time. The measured spin-echo decay time (T₂) increases systematically with nuclear polarization and is in quantitative agreement with theoretical predictions. Both the enhancement and the absolute value of the coherence time are quantitatively reproduced through cluster correlation expansion (CCE) simulations. These results establish nuclear spin hyperpolarization as a general and actively tunable approach to engineering coherence in molecular qubits. This work provides a broadly applicable design framework for high-coherence molecular and solid-state spin systems.