Integrated quantum photonics (IQP) is a promising platform for realizing scalable and practical quantum information processing. Up to now, most of the demonstrations with IQP focus on improving the stability, quality, and complexity of experiments for traditional platforms based on bulk and fiber optical elements. A more demanding question is: “Are there experiments possible with IQP that are impossible with traditional technology?”

This question is answered affirmatively by a team led jointly by Xiao-Song Ma and Labao Zhang from Nanjing University, and Xinlun Cai from Sun Yat-sen University, China. As reported in Advanced Photonics, the team realizes quantum communication using a chip based on silicon photonics with a superconducting nanowire single-photon detector (SNSPD). The excellent performance of this chip allows them to realize optimal time-bin Bell state measurement and to significantly enhance the key rate in quantum communication.

The single photon detector is a key element for quantum key distribution (QKD) and highly desirable for photonic chip integration to realize practical and scalable quantum networks. By harnessing the unique high-speed feature of the optical waveguide-integrated SNSPD, the dead time of single-photon detection is reduced by more than an order of magnitude compared to the traditional normal-incidence SNSPD. This in turn allows the team to resolve one of the long-standing challenges in quantum optics: Optimal Bell-state measurement of time-bin encoded qubits.