Silica-on-silicon waveguide quantum circuits

Quantum technologies based on photons will likely require an integrated optics architecture for improved performance, miniaturization, and scalability. We demonstrate high- fidelity silica- on- silicon integrated optical realizations of key quantum photonic circuits, including two- photon quantum interference with a visibility of 94.8 +/- 0.5%; a controlled- NOT gate with an average logical basis fidelity of 94.3 +/- 0.2%; and a path- entangled state of two photons with fidelity of >92%. These results show that it is possible to directly write sophisticated photonic quantum circuits onto a silicon chip, which will be of benefit to future quantum technologies based on photons, including information processing, communication, metrology, and lithography, as well as the fundamental science of quantum optics.