Enhancing Spin Coherence of Optically-Addressed Molecular Qubit by Nuclear Spin Hyperpolarization

TL;DR

This study demonstrates that hyperpolarizing the nuclear spin bath via triplet-DNP significantly enhances the coherence time of optically addressable molecular triplet spins, offering a tunable approach to improve quantum coherence.

Contribution

It introduces nuclear spin hyperpolarization as a novel, controllable method to extend coherence times in molecular qubits, supported by experimental and simulation results.

Findings

25% increase in spin-echo decay time with 60% proton polarization

Coherence time scales predictably with nuclear polarization

Experimental results match cluster correlation expansion simulations

Abstract

Optically addressable molecular triplet spins provide a chemically tunable platform for quantum application, but their coherence is often limited by interactions with surrounding spin baths. Here we demonstrate controlled suppression of nuclear-bath-induced decoherence in photoexcited triplet spins of pentacene co-crystallized in high-purity naphthalene single crystals. By hyperpolarizing the proton spin bath through triplet dynamic nuclear polarization (triplet-DNP), magnetic noise generated by the nuclear spins is suppressed, leading to an extension of the electron spin transverse coherence time. Experimentally, we observe a 25\% enhancement of the spin-echo decay time with $60\%$ polarization of the proton spin bath. The measured scaling of the spin-echo decay time ($T_2$) with nuclear polarization quantitatively follows the predicted dependence derived from the polarization-controlled nuclear second moment. Both the enhancement and the absolute value of the coherence time are quantitatively reproduced by 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.