W-like bound entangled states and secure key distillation

We construct multipartite entangled states with underlying W-type structure satisfying positive partial transpose (PPT) condition under any (N- 1)|1 partition. Then we show how to distill a N-partite secure key from the states using two different methods: direct application of local filtering and novel random key distillation scheme in which we adopt the idea from recent results on entanglement distillation. Open problems and possible implications are also discussed.