Diamond spin–photon interface

Spin–photon interfaces form a key building block for many quantum technologies, including quantum networks, quantum computing systems, and quantum sensing. Diamonds can host many different atomic defects whose electronic spin states can be exploited as qubits. These stationary qubits can perform local logical or sensing tasks and even couple to a range of nuclear spins acting as quantum memories or quantum registers. Through spin-selective optical transitions, this logical spin qubit can be interfaced with a flying qubit, a photon. This interface enables optical access to spin dynamics, a key capability of quantum sensors, while also allowing the generation of entangled spin–photon pairs and multiphoton cluster states, both key components of quantum networks and distributed quantum computing platforms. In this chapter, we introduce the physics of spin–photon interfaces in diamond and their practical use in a range of quantum protocols.