Catalyst: Strategic – New Zealand – Korea 2025 Joint Research Partnerships Programme

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.

Our project aims to develop a fully integrated 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. The chip will also host a complete set of active and passive photonic elements for full quantum state tomography of the squeezed output, enabling robust, turnkey operation without the need for external calibration or alignment.

Our 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. The two research teams from New Zealand and Korea bring highly complementary expertise to this collaboration: KAIST specializes in integrated lasers and photonic packaging, while the University of Auckland team contributes deep experience in optical measurement, integrated and nonlinear optics, and quantum light sources. The project will also support emerging talent through PhD and MSc positions and reciprocal researcher visits to accelerate progress and foster technical exchange.

Quantum communication networks promise ultra-secure data transmission, but current systems are limited by the short distances single photons can travel—typically tens of kilometers in fiber or line-of-sight via satellite. To extend this range, quantum repeaters are needed, and at their core lie quantum memories. However, existing quantum memories rely on bulky, free-space optics and lack integration with scalable photonic platforms. This project addresses that gap by embedding rare-earth quantum memories into photonic integrated circuits (PICs), enabling compact, scalable, and high-performance quantum repeaters. Key challenges include maintaining optical alignment at cryogenic temperatures and achieving strong light–matter interaction without damaging delicate crystal structures.

The project pioneers a hybrid architecture where light is routed through cryogenically cooled rare-earth-doped crystals using advanced photonic chips. The project will combine high-speed electro-optic modulation with long-lived quantum storage, paving the way for multiplexed quantum memories and scalable repeater nodes.

The Republic of Korea (ROK) team, led by Prof. Youngik Sohn at KAIST, brings world-class expertise in photonic integrated circuits, including high-speed modulators, multiplexers, and scalable PIC architectures. Their recent advances in electro-optic switching and ASIC integration are critical for building fast, reconfigurable quantum interfaces.

The New Zealand (NZ) team, led by Assoc. Prof. Jevon Longdell at the University of Otago, is internationally recognized for pioneering work in rare-earth-doped quantum memories. Their deep understanding of cryogenic optics and long-coherence quantum storage provides the foundation for integrating these memories into photonic platforms.

This collaboration merges complementary strengths: Korea’s advanced photonic engineering with New Zealand’s quantum memory expertise. Together, the teams will co-develop scalable quantum repeater technologies that neither could achieve alone. The partnership also facilitates technology transfer, training, and infrastructure development, particularly benefiting NZ researchers by introducing integrated photonics design and simulation capabilities. This synergy accelerates innovation and positions both countries at the forefront of quantum communication research.

This Korea–New Zealand joint research aims to establish a Quantum Communication Research Network using a hybrid interface that couples surface acoustic waves (SAW) with whispering gallery modes (WGM) in crystalline resonators. Existing quantum communication systems suffer from loss and frequency mismatch between optical and microwave domains; the project overcomes these challenges by developing a phonon–photon conversion platform enabling coherent signal transduction between heterogeneous quantum nodes.

The innovation integrates Korea’s SAW-based phonon-control and device-fabrication expertise with New Zealand’s world-leading WGM and nonlinear-optics technologies. The hybrid SAW–WGM system enables tunable photon–phonon coupling, phase control, and low-noise frequency conversion—core capabilities for future quantum repeaters and network interfaces.

Expected outcomes include quantum signal transduction (ηₜ > 50%) enabling secure communication, SAW–WGM interface modelling for quantum-network integration, and a Korea–New Zealand joint framework for quantum communication.

The project will advance the fundamental understanding of photon–phonon quantum transduction and coherent signal conversion across microwave and optical domains. It will establish an integrated Korea–New Zealand research network linking quantum acoustics and quantum photonics, enabling cross-platform interoperability and expanding the foundation for a future hybrid quantum-communication infrastructure.

The Korean team (Kyung Hee University, PI Prof. Seok-Kyun Son) specializes in SAW-based quantum devices, focusing on single-photon generation and control of phonon–photon coupling in 2D materials. The New Zealand team (University of Otago, PI Prof. Harald Schwefel & Dr. Florian Sedlmeir) brings expertise in crystalline WGM resonators, cavity optomechanics, and nonlinear optical frequency conversion. This synergy enables hybrid quantum-interface technologies that neither team could achieve alone, fostering joint publications, shared datasets, and a sustainable Korea–New Zealand research network for future quantum-communication initiatives.