High-fidelity projective read-out of a solid-state spin quantum register

Electronic and nuclear spins in solids are attractive candidates for scalable quantum information processing, but single-shot detection (which allows further key steps such as error correction and teleportation) has been achieved only for isolated qubits. Robledo et al. now demonstrate high-fidelity preparation and single-shot readout of a quantum register based on the electronic spin of a nitrogen-vacancy centre in diamond. They use this read-out to project up to three nearby nuclear spin qubits onto a well-defined state.