A solution to 2-copy distillability of Werner states
This work proves that for Werner states in any dimension $d imes d$, being 2-copy undistillable is equivalent to being 1-copy undistillable. This resolves a long-standing question about whether extracting more copies of entanglement helps with distillation for these specific quantum states. The result establishes a precise threshold where the second copy does not improve distillability.