Fig. 1

Quantum probe relaxation microscopy. a Schematic of the microscope system with optical excitation at 532 nm and resulting NV fluorescence filtered (650–750 nm) and imaged onto an sCMOS camera. Microwave control is provided via a gold microwave resonator evaporated onto a glass coverslip. Expanded view shows the diamond imaging chip with target and surface electronic spins, in addition to the layer of NV centres 7 nm below the surface. The spin lattice relaxation time, T ₁, across the imaging array is determined from a sequence of fluorescence images, see Fig. 2 for more details. b Schematic representation of the spin target hexaaqua-Cu²⁺ complex, [Cu(OH₂)₆]²⁺. c Simplified energy-level diagram for the NV centre highlighting the paramagnetic ground-state triplet. At zero magnetic field the degenerate |−1〉 and |+1〉 states are separated from the |0〉 state by the crystal field splitting of D = 2.87 GHz. d Quantum probe relaxation spectroscopy. Simplified energy diagrams representing the Zeeman splitting for a target spin (Cu²⁺) and the NV probe. When the transition energy, E _t, from the target spin (|−¹/₂〉 → |+¹/₂〉) is matched to the transition energy, E _NV, from the NV centre (|0〉 → |−1〉), the NV spin relaxation rate (1/T ₁) signal increases