During the first year of the project, the consortium has set the stage for achieving its ambitious grand goals by concentrating mainly on O1, O3 and O4. In the following, the progress towards the achievement of these objectives is summarized.
O1: IIT has developed experimental approaches for the synthesis of high-quality monolayer (ML) WS2 by CVD, from isolated single crystals to almost continuous films with size up to wafer scale (2-inch). These samples have been distributed to other project partners for further processing and characterization. UNIMIB has used high-resolution transmission electron microscopy (HRTEM) for the characterization of the defects in the pristine samples and identified single-crystal WS2 grown on pristine sapphire as the least defective material, as compared to a continuous WS2 film or WS2 grown on Al-rich sapphire. This is an important result, as it identifies the best substrate for further processing. INRS has used argon ion bombardment under high vacuum conditions for the controlled generation of defects in ML WS2. X-ray Photoelectron Spectroscopy (XPS) was then employed to characterize the defect density as a function of the fluence of the bombarding ions. A linear relationship between ion fluence and defect density was found. Further methods for defects generation such as electrochemical and proton irradiation-based approaches will be applied in the remainder of the project.
O2: while activities on this objective are scheduled to start later in the project, partner UoW initiated preliminary work on the preparation of the microcavities. Distributed Bragg Reflectors (DBRs) that define the photonic environment for the defects have been designed with the suitable central wavelength (605 nm) and bandwidth (100 nm), in order to match the resonances of defects in WS2.
O3: UU has developed numerical approaches based on density functional theory (DFT) to model point defects (both vacancies and dislocations) in ML WS2, using the Quantum Espresso (QE) code. In particular, both sulphur and tungsten vacancies have been considered and their impact on the electronic band structure and non-resonant Raman spectra has been calculated. Comparison with experimental results achieved by POLIMI and IIT is in progress. CTP PAS has performed preliminary numerical simulations of the reservoir network consisting of a network of defects in the TMD, modelling each network node (defect) as a two-level system. The defects were considered to have slightly different transition energies and decay rates and coherent coupling between nodes and linear optical coupling were assumed. The behaviour of the network was modelled upon coherent laser excitation with different values of the coupling parameter.
O4: POLIMI has implemented a widefield hyperspectral photoluminescence (PL) microscope for characterization of ML TMDs. The microscope, based on an architecture invented by POLIMI, enables acquiring spectral PL hypercubes over wide fields of view with high signal-to-noise ratio. Imaging of samples provided by IIT enabled the identification of localized metallic states introduced by the sulfur-rich zigzag terminated edges and of sulfur vacancies along the bisectors of the WS2 triangles, which are active nucleation sites.
O5: in view of this objective, to be reached at later stages of the project, UoW has developed a setup for time-resolved single-photon counting measurements, allowing the determination of the second-order correlation function, g(2). This capability is critical for assessing whether individual defects behave as isolated two-level systems and for investigating their coupling behaviour to cavity photons and adjacent defects.
O6: QUANDELA, a world-leading player in the field of photonic quantum computing, is responsible for leading the exploitation activities of the QUONDENSATE project. QUANDELA has prepared the Exploitation and Innovation Plan, which describes the Key Exploitable Results (KERs) for each partner as well as the broader impact of the project in the field of quantum computing.
