This work presents contributions to the quantum communication and in computation fields. In the area of quantum communication, we analyzed the impacts of the effects of PMD and PDL on the performance of a quantum key distribution system based on BB84 protocol in a fiber optic network. It was presented an analytical expression for the average fidelity as a function of the PMD and PDL parameters which makes possible to analyze the behavior of bit error and secure bit generation rates for a quantum communication system. In the field of quantum computing, we proposed two optical systems based on linear optics for coherent state qubits. The first system is a probabilistic generator of a four-mode-type entangled state with a maximum efficiency of 25%. From this it state was possible to propose a second system that is able to perform a probabilistically CNOT gate. Both proposed systems may be implemented with existing photonics technology. They do not use single-qubit gate or quantum teleportation that are commonly used in quantum information processing using coherent states.
Single qubit rotation gate and the controlled-NOT (CNOT) gate constitute a complete set of gates for universal quantum computation. In general the CNOT gate are only for two nearby qubits. For two qubits which are remote from each other, we need a series of swap gates to transfer these two qubits to the nearest neighboring sites, and then after the CNOT gate we should transfer them to their original sites again. However, a series of swap gates are resource for quantum information processing. One economy way which does not consume so much resource is to implement CNOT gate remotely. The remote CNOT gate is to implement the CNOT gate for two remotely separated qubits with the help of one additional maximally entangled state. The original remote CNOT gate is for two qubits, here we will present the d-dimensional remote CNOT gate. The role of quantum teleportation is identified in the process of the remote CNOT gate.