Dielectric nanoresonators and metasurfaces for photon pair generation

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Dielectric optical nanoresonators and metasurfaces constructed from such nanoresonators have been shown to enable control of light scattering, reflection and transmission. In structures with second-order nonlinearity, efficient second-harmonic generation can be used to generate classical light, with properties depending on the nanoresonators' geometry. The project nanoPAIR investigates whether such control is also possible over the quantum properties of nonclassical light generated in dielectric nanoresonators and metasurfaces. Specifically, it will investigate how the spectrum, spatial distribution, polarization, and entanglement of photon pairs generated by spontaneous parametric down-conversion (SPDC) depend on substrate materials, geometry of the nanoresonators, and their arrangement in metasurfaces.The optical properties of dielectric nanoresonators are governed by localized resonances, which can be described as superposition of multipoles and which define the local field profiles and emission directions of photons involved in SPDC. Using the multipole description, a systematic understanding of possible classical properties of the generated photon pairs, i.e. their polarization, spectrum, and emission direction, will be established based on the geometric dimensions, asymmetries, and nonlinear properties of single nanoresonators.By combining several similar nanoresonators in metasurfaces, we aim to enhance the efficiency of SPDC and obtain additional tuning parameters, e.g. lattice period mediating coupling between the nanoresonators, lattice symmetry, and orientation of nanoresonators with respect to the metasurface lattice.Understanding how to use these parameters to control SPDC will unlock the full potential of nonlinear metasurfaces for quantum state generation. We aim to achieve effective orthogonality of control parameters with respect to their influence on the properties of the photon pairs in order to realize almost arbitrary combinations of their polarization, direction, and spectrum, needed by particular applications.Our investigations will comprise analytical modelling and rigorous simulations of SPDC in nanostructures, realization of nanoresonators and metasurfaces in Aluminum Gallium Arsenide and Lithium Niobate as well as experimental verification of discovered effects.With our research, we will enable the use of metasurfaces as sources for photon pairs with a large number of spatial modes, where the properties of each mode can be tuned independently. This is notably different from other quantum source concepts allowing the generation of spatially-multimode photon pairs, e.g. bulk crystals, where the fixed crystal properties determine the possible modes that can be used. Hence, metasurfaces are promising candidates as sources for quantum-optic applications relying on many spatial modes, as e.g. high-resolution quantum imaging or free-space quantum communication with entangled vortex beams.