Li, Yi2018-03-132018-03-13b4959395xhttp://hdl.handle.net/1885/141335Quantum communication holds the promise of achieving long-distance secure message transmission by exploiting quantum entanglement between remote locations. Quantum repeaters are indispensable to the realization of quantum networks for long-distance quantum communication. Similar to its classical analogue, a good quantum repeater should be able to compensate channel attenuation with a quantum amplifier, and to combat channel distortion through a quantum equaliser. This quantum repeater should also operate by an efficient and robust protocol. The first part of this project researches the continuous mode operation of a noiseless linear amplifier (NLA). We develop a dynamical model to describe the operation of the nondeterministic NLA in the regime of continuous-mode inputs. Both the quantum scissor based NLA and the photon addition-subtraction based NLA are analysed. Simulation results are also presented to confirm theoretical analysis. The second part proposes two quantum protocols. An atomic ensemble based quantum protocol is developed to generate distributed W-states. These generated distributed W-states could be considered as an entanglement resource between more than two distant nodes and would be useful in quantum communication and distributed quantum computation in the future. We also propose a protocol by which quantum key distribution can be achieved deterministically between multiple nodes.This deterministic quantum key distribution scheme may be used to guarantee secure communication for wireless sensor networks and Internet of Things. The last project analyses distortion of quantum channels and develops physically realisable modules to combat it. The minimum phase channel and non-minimum phase all pass channel are discussed separately.enquantum communicationquantum informationquantum repeaterquantum key distributionquantum amplificationchannel equalisation201710.25911/5d6cfc3bec654