Identifying non-k-separability of a class of N-qubit complete graph   states using correlation tensors
  We derive a general expression for standard tensor norm of $N$-body correlation tensors for $N$-qubit complete graph states. With the help of this expression, we formulate a separability criterion that identifies non-$k$-separability of a class of $N$-qubit complete graph states, including GHZ state. We illustrate the performance of our criterion by considering the $N$-qubit complete graph states added with colored product noise. We also demonstrate that few local measurement settings are sufficient to evaluate our criterion. 
N. Ananth and M. Senthilvelan
quant-ph