High bit rate and operational quantum cryptography link – LIGHT

Practical metro-scale quantum communications and quantum networks over distances longer than a few tens of kilometres requires the use of single and/or entangled photons in commercial fibre cable and implementation of quantum relays. The deployment of quantum communication networks represents a challenge to which the LIGHT project brings innovative solutions. In LIGHT, world-leading team in semiconductor single-photon sources (C2N), in quantum communications (INPHYNI) and a company commercializing quantum light sources (Quandela), team up to develop the hardware and protocols for high-rate quantum communications. In a first step, we exploit the best single photon source technology with the highest rate and bring these key resources to telecom wavelength through quantum frequency conversion. In a second step, we validate our platform through a field demonstration of quantum key distribution at unprecedented rate over a three-node commercial fibre link in the South of France.
With this perspective, LIGHT aims at developing an unconditionally secured terrestrial communication link at the French scale. This will be achieved by combining complementary quantum technologies, namely innovative high-speed sources of true single photons based on semiconductor quantum dots and nonlinear sources of entangled photon pairs. The combination of individual skills will enable the development of a compact and efficient single photon source compatible with the telecommunications standard and its implementation within a quantum cryptography operational link (30km), at high speed. Finally, as a first demonstration of single photon based advanced communication protocol, we will demonstrate high-rate quantum state teleportation along a 30km fibre three node network.. .
We will tackle several technological and conceptual challenges during the project.

1 - The fabrication of a semiconductor based source of single photons at 900nm having a brightness over 90%, a sub-poissonian statistic g(2)(0) less than 10-3 as well as a repetition rate of 300MHz, exceeding by a factor 50 the current state of the art.
2 - The fabrication of a wavelength interface, in the form of an photonic chip on lithium niobate, for converting photons to the telecommunications standard with an overall efficiency greater than 50%.
3 – Unparalleled rate quantum key distribution within an existing fiber network on the French Riviera via a direct link or through a quantum relay protocol based on pairs of entangled photons already deployed between several nodes.
Each of these results will be a scientific and technological first at the international level. By combining breakthrough technology for single photon source and on-chip frequency conversion, we will demonstrate the world first telecom compliant single photon source . LIGHT is therefore a major technological step forward for the future development of quantum networks by joining the expertise of internationally renowned teams.
Finally, by working closely with Quandela, a company that markets efficient single photon sources, LIGHT ensures that technological developments are compatible with future industrial transfer. LIGHT is therefore the first step toward providing France with a key technology for large-scale quantum communications.