Nanjing University Quantum Key Distribution Network And Application

With the enhancement of computer performance,and the rapid development of quantum computers,modern cryptography encryption methods based on algorithmic complexity will be vulnerable to the attack in the future.The non-cloning theorem and uncertainty principle of quantum mechanics provide a new encryption method-Quantum Key Distribution(QKD).Although the instruments are not perfect at present,which would leave loopholes for eavesdroppers,but the key transmission protocol can guarantee the security of information transmission at physical layer aspects.It is an encryption method for future.Meanwhile methods against equipment vulnerabilities are gradually proposed.For example,decoy state is introduced in weak coherent sources to prevent photon number attack,two-photon interference measurement method is introduced to prevent the security problems from measurement devices.Quantum key distribution has been proposed since 1984,its security theory and experimental have made great progress with 36-year development.Quantum key distribution experiments have been tested in daylight free space,satellite-to-ground free space,cross-sea fiber,quantum network communication,etc.Mature communication technology has also been applied in company,such as commercial quantum key distribution equipment and commercial quantum network.Principle verification QKD experiment was performed by sending polarization encoded weak coherent photons in free space,which contained an offline post-processing program.The experiment laid the foundation for the following quantum key distribution experiments.Then we carry out tomographic protocols based on timebin encoding to characterize an installed commercial fiber network between the two campus of Nanjing University,with a fiber transmission distance of 30.5km with a loss of 12.95 d B,corresponding to 64.90 km of standard fiber.This full reconstruction of the channel helps us better understand the channel conditions.To verify the reliability of the QPT experiment,we then implement field trial of coherent one way(COW)QKD with continuous and autonomous feedback control over 12-hour.We obtain the averaged quantum bit error rates(QBERs)of 0.25% and visibilities of 99.2% respectively,matching well with the QPT results.With these field tests of our network for quantum communications,we have fully evaluated the quality of the system via both quantum state and process tomography techniques.The QPT technique can be a standardized method for calibrating the quantum fiber networks in future.We have extended a high security key rate per pulse for COW protocol over the installed commercial fiber network with a real-time feedback control.Our results pave the way for the high-performance quantum network with metropolitan fibers.As the developing of quantum key distribution technology,the QKD system is going to be faster,more miniaturization and more integration.Existing commercial companies have launched integrated commercial systems.Previous researches have shown demonstrations of QKD using photonic integrated circuits as transmitter.Here we report the realization of a relay server for measurement-device-independent QKD based on a heterogeneous superconducting-silicon-photonic chip.Thanks to the low dark count rate of the detector,the system can obtain sifted key at about 71 d B attenuation.We can measure two Bell state simultaneously in a time-bin encoding system with about 3.5ns dead time.The security key rate is improved without changing equipment.A single chip with multiple detectors in conjunction with low-loss silicon photonics are intrinsically suitable for large-scale star-like MDI-QKD network.Our experiments show the possibility of realizing a full-chip quantum key distribution system in the future.