Yifan Quan

Pentacene: excited triplet, molecular spin, polarizing agent, or quantum sensor? 

Molecular spin based quantum sensors offer a range of advantages, from high spin density to functionalization via chemical tunability. Here, we demonstrate AC vector sensing using the photoexcited spin triplet of deuterated pentacene molecules, operating at zero external magnetic field and room temperature. We achieve full three-dimensional microwave field reconstruction by detecting the Rabi frequencies of anisotropic spin-triplet transitions associated with two crystallographic orientations of pentacene in naphthalene crystals. We further introduce a phase alternated protocol that extends the rotating-frame coherence time by an order of magnitude. Additionally, we demonstrate a sizable increase in the coherence time of a pentacene electron spins by hyperpolarizing the proton spin bath via triplet dynamic nuclear polarization. The polarized nuclear spin bath provides a reduced magnetic noise environment, leading to enhanced electron spin coherence. These results establish pentacene-based molecular spins as a practical and high-performance platform for microwave sensing and nuclear spin as a practical and controllable route to engineering the platform.

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