We study a protocol for two-qubit state guidance that does not rely on feedback mechanisms. In our scheme, entanglement can be concentrated by arranging the interactions of the qubits with a continuous variable ancilla. By properly post-selecting the outcomes of repeated measurements of the state of the ancilla, the qubit state is driven to have a desired amount of purity and entanglement. We stress the primary role played by the first iterations of the protocol. Inefficiencies in the detection operations can be fully taken into account.
@article{arxiv.quant-ph/0410026,
title = {Qubit state guidance without feedback},
author = {Mauro Paternostro and M. S. Kim},
journal= {arXiv preprint arXiv:quant-ph/0410026},
year = {2009}
}