  The multiphoton states generated by high-gain spontaneous parametric
down-conversion (SPDC) in presence of large losses are investigated
theoretically and experimentally. The explicit form for the two-photon output
state has been found to exhibit a Werner structure very resilient to losses for
any value of the gain parameter, g. The theoretical results are found in
agreement with the experimental data. The last ones are obtained by quantum
tomography of the state generated by a high-gain SPDC.
