The main objective of the proposed research project is to build a diamond-based single-photon source that is capable of emitting strings of entangled photons for resource-efficient photonic quantum computing. This addresses the main challenge of measurement-based quantum computing in realising scalable multi-photon quantum information processing. We will follow recent theoretical work to realise the generation of a string of single photons that are entangled as a cluster state – the generic resource for measurement-based quantum computing.

To achieve this ambitious goal we will push current technology far beyond state-of-the-art by obtaining high light-collection efficiency from and advanced quantum control of single-photon emitters based on nitrogen-vacancy centres in diamond. To date, these light sources have been only used for obtaining individual, un-entangled photons. This will break new ground for the efficient generation of entangled photons, and will make large regions of previously inaccessible quantum state space available for modern quantum technologies.

We will develop new theory to perform feasible quantum state tomography of the emitted light by using only passive optical elements. Furthermore, we will use new experimental methods for the implementation of quantum gates; the combination of fast electro-optical switches and high-efficiency superconducting detectors will enable adaptive measurements for error correction and deterministic quantum logic operations. The results of these experiments will be crucial in the development of scalable quantum computing in realistic scenarios, and open alternative perspectives for novel applications using quantum-enhanced information technology.