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All Solid-State Super-Twinning Photon Microscope

Periodic Reporting for period 3 - SUPERTWIN (All Solid-State Super-Twinning Photon Microscope)

Periodo di rendicontazione: 2019-03-01 al 2019-10-31

SUPERTWIN's prime objective is to develop the prototype of a new microscope that exploits entangled photons to overcome the resolution limit of classical optics, at half the photon wavelength lambda/2, being lambda the wavelength of the probing light. The SUPERTWIN microscope comprises three main building blocks: (i) solid-state emitters based on advanced group-III nitride and III-V alloy epitaxial growths and wafer processing techniques to generate highly entangled photon states; (ii) CMOS single-photon detector arrays with on chip pre-processing to record spatio-temporal multi-photon interference patterns; and (iii) dedicated data processing algorithms aimed at extracting the image of the illuminated object from the statistics of scattered entangled photons. The expected achievable resolution in this case is given by lambda/2N, where N is the degree of entanglement. SUPERTWIN concept will pave the way for a new paradigm in optical imaging, triggering the development of novel microscopy systems that will surpass existing super-resolution microscopy techniques. The long-term impact of SUPERTWIN technology will be in the market of optical and scanning probe microscopy as the method is based only on the scattering properties of the specimen surface SUPERTWIN, thus enabling a multitude of applications in biology, inspection and micro/nano technology. Last but not least, a number of side results are expected from the development of SUPERTWIN building blocks, impacting on different application fields ranging from quantum optics to industrial and biomedical.
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.
Achievements and exploitable results

The main achievements are here listed:
•For the first time the OCM method to the imaging of 2-d objects showing super-resolution at the Heisenberg limit has been applied.
•A N-order correlation imaging of objects using a pseudo-thermal light source together with a time resolving detector array has been performed for the first time, in an efficient way, employing the SUPERTWIN detector. This, combined with an informational approach to image reconstruction from measured higher-order correlation functions allowed evaluation of the targeted superresolution technique;
•Efficient "sliding window" image reconstruction method able to achieve super-resolution;
•Optimization of the imaging source for better resolution
•A 60-kpixel multipurpose CMOS SPAD image sensor has been realized and fabricated, targeted for quantum imaging applications with several operating modes, not limited to time-resolved imaging but also single-bit multi-frame and counting modes.
•Demonstration and validation of Quantum-Classical Discriminator implemented with echelle grating in application to a mixed state of coherent photons and biphotons at nearly the same optical wavelengths and polarization.
•Demonstration of pulse width measurements for frequency chirped pulses using two photon interference and its implementation in a table-top setup.
•Reaching Super-Radiance in GaAs samples and showing non-classical 5-photon correlations.
•Building microscope demonstrator breadboard at classical resolution limit and magnification 70x and demonstrating resolution enhancement using correlated photon pairs
•Solitary software package for data treatment and representation of non-classical spatial correlation patterns up to the 5th order

Some of the project results have been, are or will be exploited as follows:
• A EU FET Innovation Launchpad project (GammaCam) has been obtained based on the results of the 1st SPAD array
• Partner LFOUNDRY now provides to customers the developed SPAD cells as IP blocks integrated into the PDK (process design kit)
• Scientific exploitation of experimental quantum imaging results based on 2-photon states by SPDC and higher-order correlation measurements (e.g. Nature Communications)
• One of the experimental setups is under evaluation for a patent application

Beside these outcomes and benefits, SUPERTWIN engaged experts for the Application and Exploitation Advisory Board (AEAB) and asked for an analysis and some detailed reports. The precious suggestions are being taken into account by the consortium while working towards the project objectives: in particular it is recognized that, while being in track towards the quantum superresolution microscope, the individual components that have been developed are on their own of high relevance, and contacts with industry in order to promote their commercialization is encouraged.
Microscope demonstrator with SPDC and CMOS SPAD array
Imaging at the Heisenberg limit
GaN multisection structure under test
Portable demonstrator of the 1st CMOS-SPAD array, including a source of two-photon states