Speaker
Description
Two-dimensional materials have emerged as a versatile platform for nonlinear and quantum photonic applications. In particular, rhombohedral (3R) polytypes of transition metal dichalcogenides, such as 3R-MoS$2$, feature a strong second-order nonlinear response and intrinsic C$_{3v}$ crystal symmetry. These properties allow polarization-entangled photon-pair generation through spontaneous parametric down-conversion [1], opening a way towards compact devices for quantum imaging, sensing, and metrology [2]. Whereas photon-pair rates from homogeneous ultrathin films remain low, material nanostructuring in the form of resonant metasurfaces can increase the generation rate by orders of magnitude [3]. However, only non-entangled single-polarization state generation was previously demonstrated from 2D material metasurfaces.
In this work, we reveal that the geometric phase approach to the metasurface design enables the resonantly enhanced generation of polarization-entangled states. Furthermore, the quantum states emitted by such metasurfaces can be tailored to have a different polarization structure compared to unpatterned thin films, thereby overcoming the intrinsic material limitations.
We arrange on a single metasurface arrays of nanoresonators that are rotated at a particular angle relative to each other. Such rotations introduce distinct geometric phase for the left- and right-circular polarized photons, and we show analytically that this allows flexible control over the quantum entanglement. We confirm this concept for arrays of crescent-shaped 3R-MoS$_2$ nanoresonators with 90-degree relative rotation angles, such that the metasurface rotational symmetry is intentionally distinct from that of the underlying material. Our simulations predict that a particular pump polarization produces a nearly maximally entangled biphoton state, which cannot be generated directly from an unstructured material. These principles can be generalized to a wide variety of nonlinear materials, establishing geometric-phase metasurface design as an original route toward compact, resonantly enhanced sources of polarization-entangled photon pairs for integrated quantum photonic architectures and applications.
$\small{\mathrm{[1]~M.~A.~Weissflog}~\textit{et}~\textit{al},\mathrm{~Nature~Communications}~\textbf{15},~\mathrm{7600~(2024).}}$
$\small{\mathrm{[2]~P.~A.~Moreau}~\textit{et}~\textit{al},\mathrm{~Nature~Reviews~Physics}~\textbf{1},~\mathrm{367~(2019).}}$
$\small{\mathrm{[3]~T.~Fan}~\textit{et}~\textit{al},\mathrm{~Nano~Letters}~\textbf{25},~\mathrm{11844~(2025).}}$
| I am the presenting author | Yes |
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