During the 44 months of the SUPERTWIN project, a large amount of work has been made by the consortium in order to reach the ambitious project objectives. It is not a surprise that in projects like SUPERTWIN, that aim at developing breakthrough technology, the actual activities result much more complex and partly deviate from the original plan.
The workpackage devoted to creating the foundation of the SUPERTWIN microscope concept, WP1, begun in UBE with important experimental work using SPDC bi-photons with SQ superconducting single-photon detectors (SSPD) and an already available SPAD chip from FBK, SPADnet-I. Increased correlation order measurements were performed with pseudo-thermal light sources, backing up the definition of the image reconstruction algorithms. The reconstruction was then developed and tested with correlation functions up to order 5 using CW pseudo-thermal Gaussian light sources, and the workpackage concluded with the definition of the microscope preliminary design.
The design and fabrication of one of the key components of the SUPERTWIN microscope, the solid-state sources, required an additional modelling phase, of paramount importance for the understanding of the super-radiant requirements for design. The fabrication of visible and near-infrared sources went on almost in parallel, with several iterations due to optimization of the process and design, but also to unforeseen issues and equipment failures. Nevertheless, in WP2 devices in both target wavelengths (410nm and 800nm) were successfully fabricated and tested, and extensive validation has been performed, eventually finding signatures of emission of super-radiance and non-classical light.
The quantum image sensor to be developed in WP3 went through the first iteration with a 32x32 SPAD array (called SuperEllen). The evaluation module built around it and realized in several units, allowed to perform many experiments with SPDC and pseudo thermal source, jointly with WP1 and WP4. The additional SPAD structures in a better technology and the other workpackages outcomes, formed then the basis for the concept and fabrication of the second 224×272 SPAD array (called SuperAlice) that has then been included in a SPDC setup for quantum imaging experiments.
The workpackage WP4, concerning the realization of the microscope prototype, faced the need to develop a quantum-classical discriminator (QCD) device able to separate quantum and coherent light states generated by the SUPERTWIN sources. The QCD resulted to be both a tool for the source validation and a component for the microscope. Eventually, a microscope setup integrating super-radiant sources and the SuperAlice imager would have required much more time, so the demonstrator was built with SPDC and SuperEllen, demonstrating image reconstruction beyond the classical limit.
