A five-qubit 1-resistant graph state and stabilizer marginal certificates

Abstract

We study particle-loss resistant entanglement within the framework of stabilizer and graph states. A pure state is \(m\)-resistant if it remains entangled after the loss of any \(m\) particles and becomes fully separable after the loss of any \(m+1\) particles. The smallest previously unresolved qubit case was the existence of a five-qubit \(1\)-resistant pure state, which is resolved here by the five-cycle graph state \(\ket{C_5}\). A stabilizer-subgroup method is also developed for verifying \(m\)-resistance in graph states, using local stabilizers to certify full separability and exact negative partial transpose~(NPT) witnesses to certify entanglement. Applying this to all graph states associated with non-isomorphic graphs on five, six, and seven vertices, we obtain a graph state classification up to local Clifford equivalence, which also classifies stabilizer states up to local Clifford equivalence. Thus, the five-qubit \(1\)-resistant stabilizer states are exactly the local Clifford class of \(C_5\). Six-qubit \(2\)-resistant stabilizer states exist in three distinct local Clifford classes, whereas no seven-qubit stabilizer state is \(m\)-resistant for any nonzero admissible \(m\). Finally, we prove that the cycle graph states \(\ket{C_N}\) with \(N\ge 7\) are not \(m\)-resistant for any \(0\le m\le N-2\).