Sensing Electron Spins of Copper Phthalocyanine via Relaxometry of Shallow Nitrogen-Vacancies in Diamond

Spins in molecules provide the perspectives to design robust molecular qubits with enhanced quantum coherence for sensing and computing as well as reliable scaling and integrating them into complex circuity. Compared to other solid-state spin defect qubits, the thin films of molecular qubits provide greater flexibility for reliable control over their concentration and location supporting the realization of external qubit interactions. Particularly paramagnetic metal organic molecules such as metal phthalocyanines MPc (M=Cu, Tb and Lu; Pc=C32H16N8) have recently emerged as promising platforms for quantum technologies.

In this work, by using NV’s T1 relaxometry, we demonstrate the interaction between two quantum platforms i.e. between shallow nitrogen-vacancy (NV) centers (depth ≈10 nm) and the electron spins of α-CuPc thin film (<25nm) that covers the diamond surface. By using a simple classical spin bath model to fit the results, we estimated the correlation time of CuPc’s electron spins (Cu^2+, d⁹; S=1/2), at room temperature to be 1.8ns, attributing it primarily to electron-electron spin interactions within the CuPc. By demonstrating and calibrating the interaction between CuPc and NV centers, this work demonstrates the potential of molecular qubit-NV hybrid quantum system for future quantum sensing and computing applications by combining the advantages of both quantum systems.