Focus on transformational technologies for quantum communication & semiconductor quantum devices.
World’s first open-channel TF-QKD (615km)
Fiber Loss limits the communication distance of conventional quantum key distribution (QKD) to around 400 km. Twin-field quantum key distribution (TF-QKD) can break this limit and allows secure quantum communication with favourable rate-loss scaling, but requires cumbersome interferometric implementations which are often impractical for network deployment. To resolve this problem, Zhiliang Yuan & colleagues develop a simple and versatile TF-QKD setup that can operate over an open fiber link and achieve secure communication over a distance of 615 km.
Research papers
Twin-field quantum key distribution without optical frequency dissemination
Practical inter-city key rate （5kb/s@300km）
The twin-field (TF) QKD exploits a measurement node in the middle of the
communication channel for halving the photon loss and can thus enable long-distance
secure communication. However, TF-QKD’s implementation necessitates complex
global phase tracking and requires strong phase references that not only
add to noise but also reduce the duty cycle for quantum transmission. To
resolve TF-QKD’s shortcomings but maintain its long-distance advantage,
the team implemented an innovative but simpler measurement-device-independent
(MDI) QKD that realizes repeater-like communication through post-measurement
coincidence pairing (PMP). Over 508 km optical fiber, the PMP-QKD system
delivers a finite-size SKR of 42 bit/s. Significantly, the SKR at 306 km
exceeds 5 kb/s and meets the bitrate requirement for live one-time-pad
encryption of voice communication. Compared to TF-QKD, PMP-QKD offers similar
repeater-like rate-loss scaling but has the advantage of not requiring
global phase tracking. The team’s work will bring forward economical and
efficient intercity quantum-secure networks.
Research papers
Experimental Quantum Communication Overcomes the Rate-Loss Limit without Global Phase Tracking
Compact single photon detector (700MC/s)
Our group invented a novel readout circuit (UNIC) that can effectively
suppress electronic background noise and thus enable low-noise and high-rate
single photon counting. Cascading two UNIC's in a readout circuit, the
team was able to achieve a high count rate of up to 700 MCount/s and a
low afterpulsing of 0.5 % at a detection efficiency of 25.3 % for 1.25
GHz sinusoidally gated InGaAs/InP APDs. Application to quantum key distribution
(QKD), the UNIC detectors are expected to allow a secure key rate (SKR)
exceeding 25 Mb/s over a 2 dB quantum channel. This rate would be a substantial
improvement over the state-of-the-art SKR of 13.72 Mb/s achieved with self-differencing
detectors.
Research papers
QD transparent access
Exploiting an ultra-low cavity reflectivity micropillar (0.89%), the authors
demonstrate the first observation of Mollow triplets for QDs without resort
to any laser background rejection technique. In weak excitation, we achieve
a signal to background ratio up to 55 and device responsivity of 14.4 %,
i.e., the device resonantly scattered 0.14 photons for every incident laser
photon. Raising the excitation to the few-photon level, the QD response
is brought into saturation where the authors observe the Mollow triplets
as well as the associated cascade single photon emissions. Observation
of the Mollow triplets implies the feasibility of using deterministic pulsed
excitation for efficient generation of single photons, with lossless encoding
via modulating the polarization of the excitation beam. A complete access
to the QD signal could allow excitation and collection of photons in arbitrary
polarizations, which is crucial step towards generation of photonic cluster
states.
Research papers