A Surface Molecular Qubit Scaffolded by Hexagonal Boron Nitride

Fluorescent spin qubits are central building blocks of quantum technologies. Placing such qubits at surfaces maximizes coupling to nearby spins and fields, enabling nanoscale sensing and direct integration with photonic and superconducting devices. However, reducing the dimensions or size of established qubit systems without sacrificing the qubit performance or degrading the coherence lifetime remains challenging. Here, we introduce a surface molecular qubit formed by pentacene molecules scaffolded on a two-dimensional (2D) material, hexagonal boron nitride (hBN). The spins exhibit bright fluorescence and optically detected magnetic resonance from cryogenic to ambient conditions. Using fully deuterated pentacene, the Hahn-echo coherence reaches 22 us and extends to 180 us under dynamical decoupling with multilevel control, comparable to the state-of-the-art shallow NV centers in diamond, while located directly on the surface. We map the local spin environment, resolving couplings to nearby nuclear and electron spins that can serve as auxiliary quantum resources. The hBN host further enables deterministic placement in van der Waals heterostructures, near-field integration, and chemical patterning into 2D arrays. This platform combines surface integration, long qubit coherence, and scalable fabrication, opening routes to quantum sensing, quantum simulation, and hybrid quantum devices, and is extensible to a broader family of 2D material-supported molecular qubits.