Research On Generation And Applications Of Quantum Entanglement In Telecom Band

The fusion of the basic principles of quantum mechanics and modern information technology gave birth to the interdisciplinary subject of quantum information science.At present,quantum information science has become a strategic research direction in the frontier field of information science and technology.Quantum entanglement is an important resource in quantum information science.With the rapid development of quantum information science,various entanglement application schemes including quantum teleportation,quantum entanglement exchange,quantum dense coding,quantum direct communication,quantum lighting radar,etc.,put forward higher requirements for the generation and performance of quantum entangled photon-pairs in telecom band.Although many schemes have been developed to generate entangled photon-pairs,the generation of fiber-based correlated/entangled photon-pairs with high rate and low noise in telecom band remains the key to research.In addition,in order to cooperate with different application schemes,the generation of entanglement in different degrees of freedom is also particularly important.Works in this dissertation are performed rely on the National Key Research and Development Young Scientist Project"Experimental Research on Multi-Channel Quantum Channels in Optical Communication Bands".Based on the cascaded second-order nonlinear optical process(i.e.,the second harmonic generation and spontaneous parametric down-conversion process)in Periodically Poled Li Nb O₃(PPLN)waveguide,the generation and application of quantum entanglement in the optical fiber communication band has been carried out.The generation of high-quality correlated photon-pairs and entangled photon-pairs in different degrees of freedom have been realized successively.At last,the research of quantum key distribution based on entanglement in existing optical fiber systems has been carried out.In this dissertation,a PPLN waveguide module with noise suppression filter was designed and fabricated.An experimental research platform for optical fiber communication band correlated/entangled photon-pairs based on cascaded second harmonic generation and spontaneous parametric down-conversion process has been built.The spectrum,correlation,and noise characteristics of the generated photons in the system are experimentally investigated,which lays the foundation for the generation of high-quality correlated/entangled photon-pairs.Experiment results indicate that a coincidence to accidental ratio(CAR)of 52600 could be obtained when the photon-pair generation rate is of 52.36 k Hz.Based on the generation of high-quality correlated photon pairs,through pulsed laser pumping,photon-pair coherent manipulation,etc.,quantum entanglement in different degrees of freedom can be prepared,including:energy-time entanglement,frequency-bin entanglement and time-bin entanglement.Furthermore,this dissertation has characterized entanglement by Franson interference,CHSH inequality,quantum tomography,space quantum beat and other methods.Based on the generation of high-quality entangled photon-pairs,quantum entanglement distribution and its quantum key generation application in coexistence with classical optical communication have been experimentally investigated.By using dense wavelength division multiplexing and demultiplexing technology,the coexistence scheme of quantum entanglement key distribution and classical optical communication in one 40 km-long fiber has been verified.Under different classical optical communication rates,the quantum key distribution performance has been experimentally researched.Under the condition of 40 km-long fiber transmission and the classical optical communication rate of 20 Gbps,the generation rate of quantum security keys reached 203kbps.