We study a quantum repeater which is based on decoherence free quantum gates
recently proposed by Klein et al. [Phys. Rev. A 73, 012332 (2006)]. A number of
operations on the decoherence free subspace in this scheme makes use of an
ancilla qubit, which undergoes dephasing and thus introduces decoherence to the
system. We examine how this decoherence affects entanglement swapping and
purification as well as the performance of a quantum repeater. We compare the
decoherence free quantum repeater with a quantum repeater based on qubits that
are subject to decoherence and show that it outperforms the latter when
decoherence due to long waiting times of conventional qubits becomes
significant. Thus, a quantum repeater based on decoherence free subspaces is a
possibility to greatly improve quantum communication over long or even
intercontinental distances.Comment: 22 pages, 18 figures, accepted for publication in Quantum Information
& Computatio