Alignment-tolerant hybrid integration of a diamond quantum sensor on a silicon nitride photonic waveguide

Hybrid-integrated photonic circuits play a crucial role in recent quantum technologies. However, deterministic and alignment-tolerant methods are still lacking, and their development is crucial for accelerating the scalable fabrication of quantum systems. In this study, we demonstrate alignment-tolerant coupling between diamond and silicon nitride waveguides using the deterministic transfer-printing method. To validate this approach, we also demonstrate the capability of on-chip quantum sensing using nitrogen vacancy centers in diamond waveguides. These results pave the way for compact packaging of highly sensitive quantum sensors based on photonic integrated circuits.