Amending entanglement-breaking channels via intermediate unitary operations

Cuevas, Á and De Pasquale, A. and Mari, A. and Orieux, A. and Duranti, S. and Massaro, M. and Di Carli, A. and Roccia, E. and Ferraz, J. and Sciarrino, F. and Mataloni, P. and Giovannetti, V. (2017) Amending entanglement-breaking channels via intermediate unitary operations. Physical Review A, 96 (2). 022322. ISSN 1094-1622

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    We report a bulk optics experiment demonstrating the possibility of restoring the entanglement distribution through noisy quantum channels by inserting a suitable unitary operation (filter) in the middle of the transmission process. We focus on two relevant classes of single-qubit channels consisting in repeated applications of rotated phase-damping or rotated amplitude-damping maps, both modeling the combined Hamiltonian and dissipative dynamics of the polarization state of single photons. Our results show that interposing a unitary filter between two noisy channels can significantly improve entanglement transmission. This proof-of-principle demonstration could be generalized to many other physical scenarios where entanglement-breaking communication lines may be amended by unitary filters.