Faculty of Technical Sciences

Quantum photonics is set to play an important role in future computation and communications technology. The transfer of promising lab-scale demonstrations toward scalable field-ready applications is enabled by photonic integrated circuits (PICs). In particular, mature foundry-based PIC platforms guarantee reliable and low-cost fabrication as well as high production capacity. Silicon-nitride based PICs can exhibit ultralow losses as low as 0.1 dB/m, demonstrating their suitability for integrated quantum photonics, even for nanosecond delay lines required for efficient routing of single photons.

The combination with deterministic quantum-dot based single-photon sources with high indistinguishability and purity offers the possibility for reliable generation of entangled photon states as fundamental resource for quantum computation and communications. To this end, low-loss optical switches matching the MHz to GHz single-photon generation rates are required but cannot be realized with standard components in Si₃N₄. To address this need, we have designed and optimized all-optical switches with GHz switching bandwidths based on the optical Kerr effect. The structures have been fabricated on a low-loss Si₃N₄ PIC foundry platform. Hong–Ou–Mandel measurements of on-chip Mach–Zehnder interferometers demonstrate the feasibility of the directional couplers as key components for applications in integrated quantum photonics.