Sensing of magnetic field effects in radical-pair reactions using a quantum sensor

Abstract: Magnetic field effects (MFE) in certain chemical reactions have been well established in the last five decades and are attributed to the evolution of transient radical-pairs whose spin dynamics are determined by local and external magnetic fields. The majority of existing experimental techniques used to probe these reactions only provide ensemble averaged reaction parameters and spin chemistry, hindering the observation of the potential presence of quantum coherent phenomena at the single molecule scale. Here, considering a single nitrogen vacancy (NV) centre as quantum sensor, we investigate the prospects and requirements for detection of MFEs on the spin dynamics of radical-pairs at the scale of single and small ensemble of molecules. We employ elaborate and realistic models of radical-pairs, considering its coupling to the local spin environment and the sensor. For two model systems, we derive signals of MFE detectable even in the weak coupling regime between radical-pair and NV quantum sensor, and observe that the dynamics of certain populations, as well as coherence elements, of the density matrix of the radical pair are directly detectable. Our investigations will provide important guidelines for potential detection of spin chemistry of bio-molecules at the single molecule scale, required to witness the hypothesised importance of quantum coherence in biological processes.