Electron-Nuclear Coherent Coupling and Nuclear Spin Readout through Optically Polarized V-B(-) Spin States in hBN

Coherent coupling of defect spins with surrounding nuclei along with the endowment to read out the latter are basic requirements for an application in quantum technologies. We show that negatively charged boron vacancies (V-B(-)) in hexagonal boron nitride (hBN) meet these prerequisites. We demonstrate Hahn-echo coherence of the V-B(-) spin with a characteristic decay time Tcoh = 15 mu s, close to the theoretically predicted limit of 18 mu s for defects in hBN. Elongation of the coherence time up to 36 mu s is demonstrated by means of the Carr-Purcell-Meiboom-Gill decoupling technique. Modulation of the Hahn-echo decay is shown to be induced by coherent coupling of the V-B(-) spin with the three nearest N-14 nuclei via a nuclear quadrupole interaction of 2.11 MHz. DFT calculation confirms that the electron-nuclear coupling is confined to the defective layer and stays almost unchanged with a transition from the bulk to the single layer.