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.
This advance is important not only to the field of quantum optics from a fundamental perspective, but also to quantum communications from the application perspective. The team employs the unique advantages of the heterogeneously integrated, superconducting silicon-photonic platform to realize a server for measurement-device-independent quantum key distribution (MDI-QKD). This effectively removes all possible detector side-channel attacks and thus significantly enhances the security of quantum cryptography. Combined with a time multiplex technique, the method obtains an order-of-magnitude increase in MDI-QKD key rate.
By harnessing the advantages of this heterogeneously integrated system, the team obtains a high secure key rate with a 125 MHz clock rate, which is comparable to the state-of-the-art MDI-QKD experimental results with GHz clock rate. "In contrast with GHz clock rate MDI-QKD experiments, our system doesn't require a complicated injection locking technique, which significantly reduces the complexity of the transmitter," says Xiaodong Zheng, a PhD student in Ma's group and first author of the Advanced Photonics paper.
"This work shows that integrated quantum-photonic chips provide not only a route to miniaturization, but also significantly enhance the system performance compared to traditional platforms. Combined with integrated QKD transmitters, a fully chip-based, scalable, and high-key-rate metropolitan quantum network should be realized in the near future," says Ma.
Read the open access article by Xiaodong Zheng et al., "Heterogeneously integrated, superconducting silicon-photonic platform for measurement-device-independent quantum key distribution," Adv. Photonics 3(5) 055002 (2021), doi 10.1117/1.AP.3.5.055002.