The current position：Research < Quantum Key Distribution
Quantum Key Distribution (QKD), is a secure way to distribute secret keys between the information sender and receive in a long distance. In the secure communication, secret keys are used to encrypt and decrypt information, and the security of communication is based on the security of keys. Unlike traditional ways, QKD is theoretical secure, and its safety is guaranteed by the principle of quantum physics. No-Cloning Theorem prove that an arbitrary unknown quantum state cannot be cloning perfectly. As a result, eavesdropping in a QKD system may change the quantum state itself and result in a high quantum bit error rate (QBER), which will reveal the existence of eavesdropper. Normally, transmitting quantum states is realized by encoding and detecting on single photons.
Since first being proposed in 1984, QKD has been developing for over 30 years and a lot of achievements have been done. There are breakthroughs both in theory and experiment research, not only in the original BB84 protocol based on phase or polarization encoding of single photons, but also in other protocols such as E91 protocol based on quantum entanglement, DPS protocol, COW protocol, continuous-variable protocol, measurement-device-independent (MDI-QKD) protocol, etc. Meanwhile, the research on practical QKD systems, QKD networks and QKD applications also marks that QKD the technique has been gradually put into practical use.
Our CREAM group has established a plug & play QKD system, which is the first real system to take the imperfection of laser source into account, and it also contains a real-time post-processing module. We also do research on theory problems of QKD, having discussed about the untrusted source problem in discrete-variable QKD (DV-QKD) systems and security analysis in continuous-variable QKD (CV-QKD) systems. Now, our interested directions in QKD cover the research on both theory and experiment in DV and CV-QKD, and research on MDI-QKD.
 Zhengyu Li, Yi-Chen Zhang, Feihu Xu, Xiang Peng, and Hong Guo, “Continuous-variable measurement-device-independent quantum key distribution,” Phys. Rev. A 89 (5), 052301 (2014).  Bingjie Xu, Xiang Peng, and Hong Guo, “Passive scheme with a photon-number-resolving detector for monitoring the untrusted source in a plug-and-play quantum-key-distribution system,” Phys. Rev. A 82 (4), 042301 (2010).  Xiang Peng, Hao Jiang, Bingjie Xu, Xiongfeng Ma, Hong Guo, “Experimental quantum key distribution with an untrusted source,” Opt. Lett. 33 (18), 2077-2079 (2008).