Metasurface design to control light in quantum applications

The design of metasurfaces (surfaces with sub-wavelength engineered structure) to control light in quantum applications has usually focused on classical properties, like adjusting resonances at specific frequencies. While this can improve how efficiently light is converted, it doesn’t ensure the precise control needed to produce high-quality quantum states. In an international collaboration between INRIA (France) and  the Universities of Paris, Grenoble and Strathclyde (F. Papoff and J. Jeffers) we introduce a new design approach that combines classical physics with quantum-specific goals (Advanced Optical Materials, 2026, e03793).

Instead of optimizing only for efficiency, our method directly targets important quantum properties, such as how “pure” and well-entangled the generated photons are. Using advanced optimization techniques, we simultaneously improve both the brightness of the photon source and the quality of the quantum state. Traditional designs often rely on very sharp resonances or special modes that can boost performance, but they tend to be fragile and hard to control—especially when dealing with different polarizations of light. This can lead to unwanted correlations and lower-quality entanglement.

Our approach avoids these issues, producing designs that are more stable, easier to fabricate, and deliver better overall quantum performance. When applied to a specific metasurface made of AlGaAs, our simulations predict excellent results: very high-quality entangled photon pairs (with a Bell-state fidelity close to 0.99) and a strong photon generation rate. Overall, this work provides a practical path toward compact and reliable sources of high-quality entangled photons for quantum technologies.

April 2026