Tunable Quantum Interference in Free Space with a Liquid-Crystal Metagrating
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.
Cite
@article{arxiv.2601.04947,
title = {Tunable Quantum Interference in Free Space with a Liquid-Crystal Metagrating},
author = {Maria Gorizia Ammendola and Italo Machuca Flores and Sneha Dey and Francesco Di Colandrea and Andrei Nomerotski and Bereneice Sephton and Carlo Schiano and Corrado de Lisio and Vincenzo D'Ambrosio and Lorenzo Marrucci and Patrick Cameron and Filippo Cardano},
journal= {arXiv preprint arXiv:2601.04947},
year = {2026}
}