Color centers in solid state crystals have become a frequently used system for single-photon generation, advancing the development of integrated photonic devices for quantum optics and quantum communication applications. Recently, defects hosted by two-dimensional (2D) hexagonal boron nitride (hBN) attracted the attention of many researchers around the world, due to its chemical and thermal robustness as well as high single-photon luminosity at room temperature. Unlike for NV centers in diamond and other solid-state quantum emitters in 3D systems, the 2D crystal lattice of hBN allows for an intrinsically ideal extraction efficiency, as none of the emitters are embedded in any high refractive index material and are consequently not affected by Fresnel or total internal reflection. In addition, atomically-thin crystals can be integrated into photonic circuits easily.
In this seminar I will present recent advances in developing this new type of emitter towards practical quantum information processing. The emitters can be directly integrated with fibers allowing for free-space and fiber-coupled single-photon generation. An optimized plasma etching process substantially improves the typical photophysics, achieving a narrow linewidth, high single-photon purity, and shortening of the excited state lifetime by more than one order of magnitude.Such a single-photon source, as it is compact with low size, weight and power requirements, could be used for low-cost long-distance satellite-based quantum communication, the backbone of a future quantum internet.
For this to work the photon quality needs to be further improved, which is achieved by coupling an emitter with nano-photonic structures in the Purcell regime. An increased collection efficiency and quantum yield, combined with off-resonant noise suppression and improvement of photophysics allow to use this single-photon source for realistic quantum key distribution experiments and other quantum information protocols. Furthermore, the complete device including excitation laser, driving electronics and control units is implemented on a picoclass satellite platform within a box with edge length 10cm. In parallel the single-photon emitters have been space-qualified, which was done by thermal and vacuum cycling, as well as exposure to ionizing radiation comparable to radiation levels in orbit, suggesting robust suitability for space instrumentation of 2D materials.