We study the robustness of multiparty entanglement under local decoherence, modeled by partially depolarizing channels acting independently on each subsystem. Surprisingly, we find that the robustness of (GHZ) entanglement increases with the number of qubits. An n-qubit Greenberger-Horne-Zeilinger (GHZ) state can stand more than 55% local depolarization in the limit $\overrightarrow{n}\infty .$ GHZ states are more robust than other generic states of three and four qubits. We also study spin-squeezed states in the limit $\overrightarrow{n}\infty$ and find that they too can stand considerable local depolarization.

• Received 20 September 2001

DOI:https://doi.org/10.1103/PhysRevA.65.052327