Duration: 36 months
Single- and entangled-photon emitters are essential building blocks, enabling inherently unbreakable quantum communications guaranteed by the laws of quantum mechanics. Currently, the satellite Quantum Key Distribution (QKD) communications are exclusively built with photon sources based on non-linear processes, such as spontaneous parametric down conversion in nonlinear crystals, or four-wave mixing in semiconductors. However, the number statistics of these sources is Poissonian, typically increasing error rates, requiring operation at very low intensities and implementation of QKD protocols prone to security vulnerabilities. An alternative approach is based on single-photon emitters (SPEs), such as atom-like systems, deterministically emitting a single photon on demand. The photon emission of these sources follows sub-Poissonian statistics, a pre-requisite for the most efficient quantum cryptography protocols. The optimal channel capacity is achieved with these 'true' SPEs, enabling much higher transfer rates/lower quantum bit error rates. Semiconductor quantum dots (QD) are particularly attractive, owing to their outstanding properties: bright single-photon emission, high purity, indistinguishability, entanglement fidelity. By placing an emitter in a photonic cavity, it is possible to modify the radiative decay rate and the directionality of the emission, thus cavity-enhanced quantum emitters show promise as deterministic photon sources. QKD can greatly benefit from photonic integration, which enables low-loss, alignment-free and scalable photonic circuitry. Reducing the footprint, weight and power of the QKD systems is highly desirable for space applications. On-chip integrated QD-based SPEs, low-loss waveguides and detectors will considerably reduce production costs and enable large-volume manufacturing of QKD transceivers. In this project, we will develop theoretical/modelling tools for design and optimisation of QD-cavity SPEs in the telecom wavelength range.
