It has become increasingly clear to physicists and engineers that the quantum world offers outstanding opportunities for information and communication technology applications. Examples include, among others, the implementation of protocols for secure long-distance communication and the realization of computing platforms that outperform any classical computer.

Frequently, these so-called "quantum technologies" make use of individual photon states as the fundamental unit of information. Therefore, their future success relies crucially on the availability of a device delivering indistinguishable photons on-demand, with an efficiency as close as possible to 100%. This fundamental building block for quantum technologies is known as "single-photon source" (SPS), and is currently the subject of intense investigation.

In this talk, I will discuss how to design, simulate and fabricate an SPS with an excellent performance with respect to the source efficiency, the quantum-mechanical indistinguishability of the emitted single-photon states, and their purity.
I will show the importance of designing electromagnetic cavities around an individual quantum emitter to enhance its emission rate and maximize the number of collected photons. I will also discuss how the solid-state environment deteriorates the SPS figures of merit, and how we can counteract this negative effect to protect the performance of the source.

Finally, I'll give an outline of the nano-fabrication and optical characterization techniques used to realize SPS devices, and I will examine the main experimental and theoretical challenges on the way towards optimal SPSs.