A coherent spin–photon interface in silicon

Electron spins in silicon quantum dots are attractive systems for quantum computing owing to their long coherence times and the promise of rapid scaling of the number of dots in a system using semiconductor fabrication techniques. Although nearest-neighbour exchange coupling of two spins has been demonstrated, the interaction of spins via microwave-frequency photons could enable long-distance spin–spin coupling and connections between arbitrary pairs of qubits (‘all-to-all’ connectivity) in a spin-based quantum processor. Realizing coherent spin–photon coupling is challenging because of the small magnetic-dipole moment of a single spin, which limits magnetic-dipole coupling rates to less than 1 kilohertz. Here we demonstrate strong coupling between a single spin in silicon and a single microwave-frequency photon, with spin–photon coupling rates of more than 10 megahertz. The mechanism that enables the coherent spin–photon interactions is based on spin–charge hybridization in the presence of a magnetic-field gradient. In addition to spin–photon coupling, we demonstrate coherent control and dispersive readout of a single spin. These results open up a direct path to entangling single spins using microwave-frequency photons. A single spin in silicon is strongly coupled to a microwave-frequency photon and coherent single-spin dynamics are observed using circuit quantum electrodynamics. Strong coupling in silicon Solid-state spins are promising qubits for quantum information processing thanks to their long coherence times, but harnessing spin–spin interactions is still a challenge. Spin–spin coupling is currently based on the exchange interaction and the weaker dipole–dipole interaction. Strong spin–photon coupling, achieved through coherent spin–photon interactions, could enable long-distance spin entanglement mediated by microwave photons. Here, Jason Petta and colleagues demonstrate a spin–photon interface where a single electron spin in a silicon double quantum dot is strongly coupled to a photon trapped in a microwave cavity. The technique, which relies on spin–charge hybridization in the presence of an inhomogeneous magnetic field, generates spin–photon coupling rates that ensure the coherence of the interface. The authors demonstrate all-electric control of the spin–photon coupling, as well as coherent manipulation of the spin state and dispersive readout of the single electron spin. These results suggest that a spin-based quantum processor might be one s