Silicon Photonic Chip Boosts Quantum Security

Researchers from Nanjing University and Sun Yat-sen University developed a quantum communications platform based on a silicon photonic chip with a superconducting nanowire single-photon detector (SNSPD). The chip’s performance enabled the team to realize optimal time-bin Bell-state measurement, and to significantly enhance the key rate in quantum communication.

By harnessing the unique high-speed property 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 therefore allowed the team to resolve one of the long-standing challenges in quantum optics: optimal Bell-state measurement of time-bin encoded qubits.

The advancement is important not just for quantum optics, but also for quantum communications, from an applications perspective. The team employed the advantages of the heterogeneously integrated, superconducting silicon-photonic platform to realize a server for measurement-device-independent quantum key distribution (MDI-QKD).

This effectively removed all possible detector side-channel attacks, which in turn 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.

Researchers from two universities in China developed a quantum communications platform based on a silicon photonic chip with a superconducting nanowire single-photon detector (SNSPD). A superconducting silicon chip is used as an untrusted relay server for secure quantum communication. By harnessing the low-dead-time feature of the waveguide integrated superconducting single-photon detectors (red wires with hairpin shape in the middle), optimal time-bin encoded Bell-state measurements (in blue and gray wave-like curves between four photons, indicated as red balls) are realized. These in turn enhance secure key rate of quantum communication. Courtesy of MaLab, Nanjing University.

In harnessing the advantages of this heterogeneously integrated system, the team obtained a high secure key rate with a 125-MHz clock rate.

“In contrast with GHz clock rate MDI-QKD experiments, our system does not require a complicated injection locking technique, which significantly reduces the complexity of the transmitter,” said Xiaodong Zheng, from the group of Xiao-Song Ma of Nanjing University and first author of the 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,” Ma said. “Combined with integrated QKD transmitters, a fully chip-based, scalable, and high-key-rate metropolitan quantum network should be realized in the near future.”

The research was published in Advanced Photonics (www.doi.org/10.1117/1.AP.3.5.055002).