Room-temperature entanglement between single defect spins in diamond

Entanglement is the central yet fleeting phenomenon of quantum physics. Once being considered a peculiar counter-intuitive property of quantum theory(1), it has developed into the most central element of quantum technology. Consequently, there have been a number of experimental demonstrations of entanglement between photons(,)(2) atoms(3), ions(4) and solid-state systems such as spins or quantum dots(5-7), superconducting circuits(8,9) and macroscopic diamond(10). Here we experimentally demonstrate entanglement between two engineered single solid-state spin quantum bits (qubits) at ambient conditions. Photon emission of defect pairs reveals ground-state spin correlation. Entanglement (fidelity = 0.67 +/- 0.04) is proved by quantum state tomography. Moreover, the lifetime of electron spin entanglement is extended to milliseconds by entanglement swapping to nuclear spins. The experiments mark an important step towards a scalable room-temperature quantum device being of potential use in quantum information processing as well as metrology.