Quantum photonics with metamaterials

Photons, the particles of light, play a crucial role in nearly all quantum technology platforms, as they are ideal carriers of quantum information. However, the optical elements used in these quantum systems remain conventional, relying on bulky optics such as lenses, beam splitters, wave plates, and mirrors, which are either unsuitable or suffer from poor scalability. Recent advances in metamaterials, particularly metasurfaces, are driving a transformative shift in quantum photonics. Metasurfaces, composed of one or a few layers of tailored nano-resonators, offer unprecedented flexibility in controlling light across all degrees of freedom, combining miniaturization with scalability. This lecture will explore how these artificially engineered materials and nanostructures can be designed and manufactured to facilitate the generation, manipulation, and measurement of quantum states of light. Specifically, I will present examples from our research that demonstrate the use of nanostructured metasurfaces to perform quantum state tomography for photons, achieve nontrivial transformations of entangled photonic qubits, and conduct quantum state discrimination. These examples will highlight how the latest advances in nanotechnology are reshaping the fundamental building blocks of optical elements in quantum science and technology.

Kai Wang joined the faculty of McGill University in January 2023 as an assistant professor and holder of a research chair startup fund in quantum photonics supported by the Ministère de l'Économie, de l'Innovation et de l'Énergie du Québec. Before joining McGill, he was a postdoctoral researcher at Stanford University (2020-2022). Before that, he received his PhD in physics from the Australian National University in 2019. Kai Wang's research program mainly focuses on metasurfaces for quantum photonics and non-Hermitian topological quantum photonics. He did pioneering or highly impactful works in both fields, including the demonstration of a sub-wavelength-thin metasurface for multiphoton state manipulation and measurement [K. Wang et al. Science 361, 1104 (2018)] and the demonstration of non-Hermitian point-gap topology [K. Wang, et al., Science 371, 1240 (2021)] as well as braid-group topology [K. Wang, et al., Nature 598, 59 (2021)] in synthetic dimensions of photonic systems. He holds multiple prizes and organizations, such as a winner of the 2024 Optica Foundation Challenge and the 2019 Warsash Science Communication Prize in Optics from the Australian Optical Society.