Graph‑Engineered Metasurface Packs Quantum Optics onto a Single Chip

Quantum photonics promises room‑temperature quantum computers and ultra‑secure networks, yet today’s systems still rely on bulky forests of lenses, mirrors, and beam splitters that are hard to scale. Kerolos M. A. Yousef and colleagues in the Capasso and Loncar groups have now engineered an ultrathin metasurface whose graph‑theory‑guided design of meta‑atoms compresses an entire linear‑optical network onto a single chip, entangling photons and enabling generalized Hong–Ou–Mandel interference. Reported in Science on 24 July 2025, the device delivers alignment‑free, low‑loss, room‑temperature operation with no moving parts. Robust, cost‑effective, and fully compatible with standard lithography, this compact platform charts a practical course toward scalable quantum processors, chip‑scale sensors, and “lab‑on‑a‑chip” quantum technologies that leave bulk optics behind.

Read the paper here, or checkout the perspective article in Science here, and the Harvard press release here. 

Image credit: Joshua Mornhinweg