Dielectric nanoresonators and metasurfaces for photon pair generation

由这种纳米谐振器构成的介电光学纳米谐振器和亚表面已经被证明能够控制光的散射、反射和传输。在具有二阶非线性的结构中，有效的二次谐波产生可以用来产生经典光，其性质取决于纳米谐振器的几何形状。纳米PAIR项目研究是否也可以对介电纳米谐振器和亚表面中产生的非经典光的量子特性进行控制。具体地说，它将研究自发参数下转换(SPDC)产生的光子对的光谱、空间分布、偏振和纠缠如何依赖于衬底材料、纳米谐振器的几何形状以及它们在亚表面上的排列。介质纳米谐振器的光学性质受局域共振控制，局域共振可以描述为多极的叠加，它定义了SPDC中涉及的光子的局域场分布和发射方向。利用多极描述，基于单个纳米谐振器的几何尺寸、不对称性和非线性特性，系统地了解产生的光子对可能的经典性质，即偏振、光谱和发射方向。通过将几个类似的纳米谐振器组合在亚表面上，我们的目标是提高SPDC的效率，并获得额外的调谐参数，如晶格周期调节纳米谐振器之间的耦合，晶格对称性，以及纳米谐振器相对于亚表面晶格的取向。理解如何利用这些参数来控制SPDC，将释放非线性亚表面产生量子态的全部潜力。我们的目标是根据控制参数对光子对性质的影响实现有效的正交性，以实现特定应用所需的几乎任意的偏振、方向和光谱组合。我们的研究将包括纳米结构中SPDC的解析建模和严格模拟，在砷化铝和铌酸锂中实现纳米谐振器和亚表面，以及对已发现的效应进行实验验证。通过我们的研究，我们将能够使用亚表面作为具有大量空间模的光子对的源，其中每个模的性质都可以独立调节。这明显不同于允许产生空间-多模光子对的其他量子源概念，例如大块晶体，其中固定晶体属性确定可以使用的可能模式。因此，亚表面很有可能成为依赖于许多空间模式的量子光学应用的候选光源，例如高分辨率量子成像或纠缠涡旋光束的自由空间量子通信。

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.