The possibility to monitor and to control spin coherences within single molecules would provide unprecedented sensitivity in molecular structural analysis (i.e., NMR/EPR spectroscopies and imaging) and enable new ways to drive spin-dependent and chiral-selective chemistries. To this end, shallow nitrogen–vacancy (NV) centers in diamond have emerged as a promising platform to measure localized magnetic fields and to drive spin dynamics in adsorbed molecules. Manipulated by light and microwave pulses, the fluorescent NV center can be exploited as a room-temperature-accessible “meter” qubit to probe spin coherences via optically detected magnetic resonance. However, tracking spins with atomic spatial resolution in molecular adsorbates remains a challenge. More generally, the sensing capability of near-surface NVs is severely limited by charge state instabilities and decoherence due to surface traps and electronic/magnetic noise, respectively. Here, we report on strategies to overcome these issues by controlled termination and functionalization of the diamond surface to bind molecules of interest while decoupling shallow NVs from charge traps and surface noise. Measuring the optical readout from single NV centers, we track the chemical functionalization of oxygen- and nitrogen-terminated diamond surfaces. We probe 1H and 19F nuclei of dilute assemblies of adsorbed molecules via their hyperfine coupling to the electronic spin of underlying NVs. By optimizing the surface chemistry and optical detection protocols, we take an important step forward toward realizing the precise quantum control of nuclear and electronic coherences at the single-molecule level.

Probing quantum spin coherence in adsorbed molecules with shallow NV centers in diamond

ACS Fall 2021

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