Room-temperature polarization of individual nuclear spins in diamond via anisotropic hyperfine coupling and coherent population trapping

Abstract

Abstract We employ the electronic spin of a single nitrogen-vacancy (NV) defect in diamond to detect and control the quantum state of remote nuclear spins coupled by hyperfine interaction. More precisely, our work focuses on individual $$^{13}\text {C}$$ 13 C nuclei featuring a moderate hyperfine coupling strength ($$\sim 1$$ ∼ 1  MHz) with the NV’s electron spin. Two different methods providing an efficient room-temperature polarization of these peculiar $$^{13}\text {C}$$ 13 C nuclear spins are described. The first one is based on a polarization transfer from the NV electron spin to the $$^{13}\text {C}$$ 13 C nucleus, which is mediated by the anisotropic component of the hyperfine interaction. The second one relies on coherent population trapping (CPT) within a $$\Lambda $$ Λ -type energy-level configuration in the microwave domain, which enables to initialize the $$^{13}\text {C}$$ 13 C nuclear spin in any quantum state superposition on the Bloch sphere. This CPT protocol is performed in an unusual regime for which relaxation from the excited level of the $$\Lambda $$ Λ -scheme is externally triggered by optical pumping and separated in time from coherent microwave excitations. For these two polarization techniques, we investigate the impact of optical illumination on the nuclear spin polarization efficiency. This work adds new methods to the quantum toolbox used for coherent control of individual nuclear spins in diamond, which might find applications in quantum metrology. Graphical Abstract