Towards magnetic resonance imaging of a single molecule.*

While magnetic resonance is an established tool for applications ranging from molecular structure determination to quantum computing, it typically requires large ensembles of molecules to detect the weak magnetic signals. In order to push magnetic resonance spectroscopy and control to the single-molecule limit, we magnetically couple spin-carrying metal-organic complexes to the electron spin of an individual nitrogen-vacancy (NV) defect in diamond, which can be optically initialized and read out. The electron spin on the coordinated metal acts as a reporter of the nuclear spin positions on the complex or a target of interest attached to it, promising to extend electron paramagnetic resonance spectroscopy (EPR) to the limit of single-molecule magnetic resonance imaging (MRI). In addition, the complex can be coherently controlled via the NV center and act as a molecular qubit, which can be assembled into desired quantum spin network architectures via chemical linking.