Light sources producing large numbers of entangled photons are key for the future development of optical quantum technologies. They could be the backbone of high rate quantum networks, the key ingredient for the development of large-scale universal optical quantum computers or simulators, and would find numerous applications in quantum metrology. However, entangled-photon sources that are truly scalable in photon number are not existing to date, since, all traditional entangled-photon sources operate probabilistically, which leads to an unfortunate scaling beyond a few photons.
In QLUSTER we join experts in many-particle entanglement, single photon sources, coherent control of spins in quantum dots and spin-photon entanglement to develop a deterministic source of 20 or more entangled photons.
The underlying idea is simple: if the polarization of one photon can be entangled with the spin of an electron in a quantum dot, this process can be repeated to entangle many photons. Practical implementation, however, is very challenging since high-fidelity devices have to be developed, high-quality optical cavities are needed for efficient photon extraction, novel protocols have to be developed, and so on. But the prospects are exciting, we hope to develop a resource that has real potential to revolutionize photonic quantum technologies, and therefore the emerging quantum computing, simulation and networking efforts.