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arXiv · 2601.04947

Tunable Quantum Interference in Free Space with a Liquid-Crystal Metagrating

Maria Gorizia Ammendola·Italo Machuca Flores·Sneha Dey·Francesco Di Colandrea·Andrei Nomerotski·Bereneice Sephton·Carlo Schiano·Corrado de Lisio·Vincenzo D'Ambrosio·Lorenzo Marrucci·Patrick Cameron·Filippo Cardano
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Abstract

Structured optical materials provide a promising platform for photonic quantum information processing in free space. Beam splitters, a fundamental building block of photonic circuits, have recently been demonstrated in free space using geometric-phase optical elements. These devices coherently mix circularly-polarized transverse modes of freely-propagating optical fields, including modes carrying orbital angular momentum. In this work, we investigate liquid-crystal metagratings as electrically tunable beam splitters for transverse-momentum optical modes. By exploiting the voltage-controlled birefringence of liquid-crystal metasurfaces, we experimentally tune the splitting ratio of the device and thereby control the degree of two-photon interference between indistinguishable photons. At the output, photons are spatially resolved on different regions of a time-resolved single-photon-sensitive detector, enabling the reconstruction of coincidence maps in the Fourier plane. This approach is readily scalable and enables highly parallel coincidence measurements across a large number of optical modes.

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Maria Gorizia Ammendola, Italo Machuca Flores, Sneha Dey, Francesco Di Colandrea, Andrei Nomerotski, Bereneice Sephton, Carlo Schiano, Corrado de Lisio, Vincenzo D'Ambrosio, Lorenzo Marrucci, Patrick Cameron, Filippo Cardano. 2026-01-08. Tunable Quantum Interference in Free Space with a Liquid-Crystal Metagrating. https://arxiv.org/abs/2601.04947

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