Scientists world-wide are in pursuit of radical proposals to exploit coherent quantum states for a diverse range of applications including communication, information processing, and metrology. Similar to conventional technologies, the quantum machinery will most likely consist of photons and semiconductor devices to create, transmit, receive, and process the quantum information. The ingredients of the ideal solid-state quantum photonic platform are:
- Ultra-stable (coherent) quantum emitters with large oscillator strengths. This enables robust generation of indistinguishable single photons, an essential resource for many quantum technologies.
- The ability to intra-convert coherent single (pseudo-)spins and photons. This enables spin-photon entanglement and underpins quantum repeaters, essential for quantum communication networks.
- Integrated electronic and photonic functionality. This allows full emitter and spin control and opens routes to scalability via integrated technologies. Self-tuning and automatic optimisation are also crucial ingredients for a scalable and robust architecture.
A range of solid-state single quantum emitters have been developed over the last few decades. Leading systems include crystal defects in diamond or SiC, III-V self-assembled quantum dots, or rare earth ions doped into insulating materials. Each quantum material platform has established clear-cut benefits and drawbacks. For instance, III-V quantum dots have the best prospects for indistinguishable single photon generation but defects in wide bandgap materials have the most robust spin. Rare earth ions doped solids have unique potential as multiplexed quantum devices for the generation and the storage of quantum states of light.
We also investigate an intriguing alternative host for a quantum emitter: a two-dimensional semiconductor, which offers tantalizing potential for new physics and potential technologies.