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

TL;DR

This paper demonstrates high-visibility Hong-Ou-Mandel interference using telecom photons in a lithium niobate on insulator (LNOI) directional coupler, advancing integrated quantum optics for scalable quantum technologies.

Contribution

It is the first to realize HOM interference in an LNOI directional coupler with near-perfect beam splitting and high visibility, enabling integrated quantum experiments.

Findings

Achieved 93.5% HOM visibility in LNOI device

Designed and fabricated a balanced directional coupler in LNOI

Confirmed good agreement with off-chip measurements

Abstract

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+/-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