Research

Research - Quantum Photonics

Our group pursues two interconnected research directions at the frontier of quantum photonics: quantum communication, spanning long-distance quantum key distribution to chip-scale photonic integration; and quantum dot and cavity QED, exploring the fundamental physics and quantum information applications of single quantum emitters in engineered optical cavities.

Quantum Communication

Quantum communication provides a foundation for provably secure links and distributed information processing over long distances. Our research focuses on practical quantum networks, from long-distance QKD to high-speed photonic devices and chip-scale integration.

A central focus is twin-field QKD (TF-QKD), which places a measurement node at the midpoint of the channel to overcome the fundamental rate-loss limit of conventional QKD. We demonstrated the world's first open-channel TF-QKD system, achieving secure communication over 615 km without optical frequency dissemination, and validated the approach in a 546 km field trial using independent optical frequency combs. To simplify deployment, we developed a post-measurement coincidence pairing (PMP) scheme that retains repeater-like rate-loss scaling while eliminating global phase tracking, achieving 5 kb/s at 306 km — sufficient for live voice encryption. We have also demonstrated high-rate measurement-device-independent QKD without optical reference light, quantum fingerprinting without the shared randomness loophole, and fiber-integrated quantum frequency conversion for long-distance quantum networking.

At the device level, we invented the UNIC readout circuit for InGaAs/InP avalanche photodiodes, enabling count rates up to 700 Mcount/s with low afterpulsing — supporting secure key rates exceeding 25 Mb/s. On the photonic integration side, we have developed low-loss lithium niobate and silicon chip platforms for QKD, bright heralded single-photon sources, chip-based entangled photon pair sources, and demonstrated high-rate entanglement swapping between independent on-chip sources — key building blocks for scalable quantum network architectures.

Research papers

Quantum Dot and Cavity QED

Single quantum dots in engineered optical cavities provide a uniquely rich platform for exploring light–matter interaction at the quantum level, generating non-classical states of light, and producing entangled photons for quantum information applications.

A key enabling innovation is our quantum dot micropillar device with an ultra-low cavity reflectivity of just 0.0089 and a Purcell factor of 10.9, which provides transparent access to the resonance fluorescence signal without any laser background rejection and brings the emitter into the few-photon saturation regime. Beyond the micropillar, we have developed novel cavity geometries — a topological bulk cavity offering robust Purcell enhancement against fabrication imperfections, and an anisotropic Dirac cavity enabling deterministic polarised single-photon emission without the efficiency penalty of polarisation filtering. We have also demonstrated a cavity-enhanced two-photon emitter via dark-state biexciton loading, achieving a two-photon fraction of 98.3% — a deterministic solid-state source of photon pairs with high purity.

At the heart of our quantum dot programme is a unified model of resonance fluorescence, in which all scattered photons are treated as spontaneous emission events within a pure joint quantum state of the emitter and photon field. This single picture simultaneously explains two properties long thought to require separate descriptions: the laser-like linewidth and the persistent photon antibunching. The model makes quantitative predictions — confirmed experimentally — for the coherence and photon statistics of the emission across all excitation regimes, from the Heitler limit to the Mollow triplet. Building on this foundation, we demonstrated that resonance fluorescence can be transformed, using an asymmetric interferometer, into two-photon energy-time entanglement, with both the simultaneous two-photon and the temporally separated photon-pair sectors independently violating Bell's inequality — establishing resonance fluorescence from a solid-state emitter as a versatile, scalable resource for quantum information.

Research papers