Chip-integrated high-fidelity squeezed light source for secure quantum communication

Quantum communication systems derive their security from the fundamental laws of quantum mechanics, offering absolute protection against eavesdropping. This intrinsic security has made quantum key distribution (QKD) a highly attractive solution for government agencies and financial institutions seeking to safeguard their most sensitive data. However, currently deployed systems are typically composed of bulky transmitters and receivers that contain many delicate optical components, all of which must be precisely packaged and aligned.

This project aims to develop a fully integrated quantum key distribution (QKD) laser source, with all critical components monolithically fabricated on a single 1 cm² silicon-nitride chip. Central to our design is an on-chip optical parametric oscillator (OPO) ‘squeezer’ circuit, engineered to transform the input laser light into the correct quantum state required for a high performance QKD protocol known as continuous-variable (CV) QKD. Unlike discrete-variable implementations, CV-QKD offers higher bitrates and better compatibility with existing telecommunications infrastructure. This project lays the foundations for future wafer-scale mass fabrication of QKD sources, an essential step toward low-cost, large-scale deployment of quantum communication networks.

To realise this design, it is proposed to develop a new type of hybrid integrated optical circuit. This hybrid architecture promises to enable a unique combination of both low propagation loss and high nonlinear efficiency.  This fully on-chip system will then be fully characterised with the goal of approaching performance levels currently only attainable in laboratory-scale tabletop systems.

The two research teams from New Zealand and the Republic of Korea bring highly complementary expertise to this collaboration. Korea’s Advanced Institute of Science & Technology team specialises in the fabrication of integrated lasers, photonic integrated circuits (PICs), and photonic packaging, and has access to KAIST’s world-class fabrication facilities. The University of Auckland team contributes deep experience in optical measurement, integrated and nonlinear optics, quantum measurement and quantum light sources.