February 28th 2025

LISE 303 12pm-1pm

Abstract: Metasurfaces—subwavelength arrays of spatially varying nanostructures—are transforming optics by offering flat, ultra-thin alternatives to bulky devices. By locally tailoring the phase, polarization, and other properties of light at each meta-atom, these nanotextured surfaces have enabled the miniaturization of key optical components such as metalenses (flat lenses), holograms, axicons, and specialized polarization elements. Crucially, by allowing the metasurfaces to manipulate more than one degree of freedom simultaneously—like phase and dispersion, or momentum and polarization—they unlock system-level miniaturization, eliminating the need for multiple lenses or complex setups. This has led to remarkable innovations, from dispersion-engineered metasurfaces that replace multi-material lens cascades to polarization cameras that directly capture polarization information of a scene in a single shot.

In this talk, I will discuss how these advances in metasurfaces can be extended to the quantum domain, focusing on whether a single metasurface can replace conventional beam-splitter networks used to manipulate non-classical states of light—crucial for quantum computing and other quantum technologies. Through a combination of theory and experiment, I will show the subwavelength engineering of each meta-atom’s matrix-valued transformation can induce strong multipath interference, enabling simultaneous multiphoton bunching, antibunching, and entanglement. I will also introduce a dual graph-theoretic framework that visually captures both the metasurface’s transformations and the quantum correlation landscape they produce. Building on this insight, I will illustrate how this duality can be leveraged to map conventional linear quantum optical circuits onto a single metasurface layer, thereby eliminating the quadratically growing hardware overhead. Ultimately, this approach establishes a new
paradigm for scalable, low-decoherence quantum photonic infrastructure.

About the speaker: Kerolos M. A. Yousef is a Ph.D. candidate in Applied Physics at Harvard University.
His current research explores innovative approaches to utilizing metasurfaces for quantum photonics, and for manipulating non-classical states of light. In 2018, during his sophomore year, Kerolos spent a year in the Capasso Lab, where he contributed to the development of dispersion-engineered metasurfaces for compact imaging and spectroscopy applications.