Demonstration of Hong-Ou-Mandel interference in an LNOI directional coupler

Interference between single photons is key for many quantum optics experiments and applications in quantum technologies, such as quantum communication or computation. It is advantageous to operate the systems at telecommunication wavelengths and to integrate the setups for these applications in order to improve stability, compactness and scalability. A new promising material platform for integrated quantum optics is lithium niobate on insulator (LNOI). Here, we realise Hong-Ou-Mandel (HOM) interference between telecom photons from an engineered parametric down-conversion source in an LNOI directional coupler. The coupler has been designed and fabricated in house and provides close to perfect balanced beam splitting. We obtain a raw HOM visibility of (93.5 & PLUSMN; 0.7) %, limited mainly by the source performance and in good agreement with off-chip measurements. This lays the foundation for more sophisticated quantum experiments in LNOI.& COPY; 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

Interference between single photons is crucial for various quantum optics experiments and applications in quantum technologies like communication and computation. Using lithium niobate on insulator (LNOI) as a new material platform for integrated quantum optics allows for operation at telecommunication wavelengths and integration of setups for improved stability, compactness, and scalability. By implementing a Hong-Ou-Mandel (HOM) interference in LNOI directional coupler, we achieve a high raw HOM visibility of (93.5 ± 0.7)%, establishing the foundation for advanced quantum experiments in LNOI.