What are single photons good for?

TL;DR

This paper challenges the common belief that single-photon sources are essential for quantum technologies, showing they are unnecessary for some tasks but crucial for future advancements like device-independent security and long-distance quantum communication.

Contribution

It demonstrates that single-photon sources are not needed for point-to-point quantum key distribution but are vital for advancing secure and long-distance quantum communication technologies.

Findings

Single-photon sources are not necessary for quantum key distribution using faint laser pulses.

Single-photon sources can enable device-independent quantum security.

They can extend quantum communication distances to hundreds of kilometers.

Abstract

In a long-held preconception, photons play a central role in present-day quantum technologies. But what are sources producing photons one by one good for precisely? Well, in opposition to what many suggest, we show that single-photon sources are not helpful for point to point quantum key distribution because faint laser pulses do the job comfortably. However, there is no doubt about the usefulness of sources producing single photons for future quantum technologies. In particular, we show how single-photon sources could become the seed of a revolution in the framework of quantum communication, making the security of quantum key distribution device independent or extending quantum communication over many hundreds of kilometers. Hopefully, these promising applications will provide a guideline for researchers to develop more and more efficient sources, producing narrowband, pure and indistinguishable photons at appropriate wavelengths.