An Australian research team has successfully developed a new tunable entangled photon-pair generation technology using an indium gallium phosphide (InGaP) metasurface. The achievement, completed by researchers from the Department of Electronic Materials Engineering (EME) and the ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), has been published in Science Advances.

By adjusting the crystal orientation of the InGaP metasurface and leveraging its nonlinear optical properties, the team achieved on-demand control of photon-pair entanglement. Team leader Professor Andrei Sukhorukov stated: "This is the first time the asymmetry of a metasurface has been used to dynamically regulate entangled photon pairs." Experiments showed that, by varying the pump laser wavelength, the polarization entanglement of the photon pairs can switch from fully entangled to completely unentangled on a picosecond timescale.

The core of the technology lies in the special structural design of the metasurface. Co-lead author Dr. Tuomas Haggren noted: "The wide bandgap of InGaP gives it excellent optical performance in the red-light spectrum." The team employed [110]-oriented growth technology combined with a 500-nanometer-high micropillar array structure, significantly boosting photon-pair generation efficiency. Measurements showed a signal-to-noise ratio two orders of magnitude higher than that of conventional semiconductor optical devices.

This breakthrough provides a more flexible source of entanglement for quantum communication and cryptography. Co-first author Dr. Ma Jinyong said: "The compactness and fast tunability of metasurfaces make them highly promising for integrated quantum optical systems." Furthermore, the technology can be extended to multi-degree-of-freedom entanglement control, opening new pathways for the preparation of hyper-entangled states.