Quantum communication in noisy environments

In this thesis, we investigate how protocols in quantum
communication theory are influenced by noise. Specifically, we take
into account noise during the transmission of quantum information
and noise during the processing of quantum information. We describe
three novel quantum communication protocols which can be
accomplished efficiently in a noisy environment: (1) Factorization
of Eve: We show that it is possible to disentangle transmitted
qubits a posteriori from the quantum channel's degrees of freedom.
(2) Cluster state purification: We give multi-partite entanglement
purification protocols for a large class of entangled quantum
states. (3) Entanglement purification protocols from quantum codes:
We describe a constructive method to create bipartite entanglement
purification protocols form quantum error correcting codes, and
investigate the properties of these protocols, which can be
operated in two different modes, which are related to quantum
communication and quantum computation protocols, respectively.