Work Plan

The project contains 4 work packages (WPs) described in the following with sequential objectives, maximising the partners collaboration in the SPS fabrication, theory support for SPS optimal RT performance, their competitive use in free-space, metropolitan quantum communication protocols (also assisted with theory) and the eventual deployment of the project technology in the quantum industry (through the consortium companies, NAN, and QLD). The Gantt Chart represents the working timeline in Fig. 5, and the coherent cooperation among the members is sketched in the Pert Chart in Fig. 6.

WP1: Fabrication of RT-SPSs based on an electrically driven open cavity coupled to hBN emitters (UOL, NAN, UAM, UOB). 

In this WP, UOL will develop the deterministic implantation of hBN defects targeting consistent emission wavelengths and defect species. This will simultaneously be de-risked by identifying suitable SPEs formed from defects in commercially available hBN flakes. The cavity mirrors will present a double nanofabrication (UAM, UOL): (1) focused-ion-beam milling of micrometric lenses, allowing for the confinement of a single optical mode in the cavity, (2) sputtering growth of dielectric DBRs (pairs of SiO2/TiO2). An electrically driven GaInP LED (NAN) will be integrated in the bottom mirror to emit non-resonant pulses of light, exciting the hBN defects. Final cavity designs will be informed by FDTD simulations (UOB) which will have to be simultaneously optimised to ensure optimum excitation of the SPE by the LED, along with efficient collection of the single photon output. The open cavity system will be assembled with a titanium cage (UOL, UAM) in a setup for optimal collection efficiency of single photons.

WP2: High-performance of RT-SPS in brightness and purity (IIT, UAM, UOL, TUB, UOB, NAN). 

The developed RT-SPS device in UAM/UOL will be transferred to IIT/TUB for the next project steps. IIT will coordinate the experiments to study the performance of the RT-SPS. In a first part, IIT will study the spectral characteristics of the SPE (spectral range of defect lines, emission linewidth, spectral stability), dedicating special attention to defects matching the Fraunhofer lines laying in the spectral window to the hBN emission; lifetime studies will determine the Purcell enhancement induced by the open cavity; finally, polarisation-resolved studies will determine the degree of linear polarisation exhibited by the SPE, fundamental in the QKD protocol.15 The results obtained by IIT will assist UOB to iterate the simulations of cavity design. In a second stage of the WP, measuring the brightness and purity under electrical driving (UOL, TUB, NAN) will allow us to determine the performance of the RT-SPS, and select the best performant defects for the next WP3. Theory simulations (IIT, UOB) will follow the experiments on the SPE physics (three-level system emission, non-radiative or re-excitation processes, etc).

WP3: Quantum Communication using high-performance RT-SPSs (TUB, IIT, UOL, UAM QLD, NAN). 

In the last scientific WP, we employ the RT-SPS in implementations of BB84- and B92-QKD, both in laboratory and field experiments. At the laboratory-scale, we aim to achieve record-high secure key rates of ~100 kbits/s. For the field implementation, we use a telescope-based FSO quantum link in Berlin city bridging a record distance of ca. 750 m (double-pass configuration), with the perspective to further extend the link distance to ca. 0.6/1.2 km distance, setting a record in metropolitan FSO-link BB84/B92-QKD with sub-poissonian sources.17,20 In the last stage of the WP3, a market study of the RT-SPS and various QKD applications and a possible commercialisation of the device will be implemented by QLD assisted with NAN.

WP4: Management, dissemination, exploitation (UAM, all). 

The UAM will take charge of organizing the workflow, creating an exploitation plan in collaboration with all partners, and overseeing the dissemination activities during the whole development of COMPHORT.