The stabilizer for..-qubit symmetric states

The stabilizer group for an n-qubit state |Φ is the set of all invertible local operators(ILO) g = g1g2···gn,gi 2 GL(2,C) such that |Φ= g|Φ. Recently, Gour et al. [Gour G, Kraus B and Wallach N R 2017 J. Math. Phys. 58092204] presented that almost all n-qubit states jyi own a trivial stabilizer group when n≥5. In this article, we consider the case when the stabilizer group of an n-qubit symmetric pure state jyi is trivial. First we show that the stabilizer group for an n-qubit symmetric pure state |Φ is nontrivial when n≤4. Then we present a class of n-qubit symmetric states |Ψ with a trivial stabilizer group when n≥5. Finally, we propose a conjecture and prove that an n-qubit symmetric pure state owns a trivial stabilizer group when its diversity number is bigger than 5 under the conjecture we make, which confirms the main result of Gour et al. partly.     

Monogamy relations of quantum entanglement for partially coherently superposed states

Monogamy is a fundamental property of multi-partite entangled states. Recently, Kim J S [ Phys. Rev. A 93 032331]showed that a partially coherent superposition(PCS) of a generalized W-class state and the vacuum saturates the strong monogamy inequality proposed by Regula B et al. [ Phys. Rev. Lett. 113 110501] in terms of squared convex roof extended negativity; and this fact may present that this class of states are good candidates for studying the monogamy of entanglement. Hence in this paper, we will investigate the monogamy relations for the PCS states. We first present some properties of the PCS states that are useful for providing our main theorems. Then we present several monogamy inequalities for the PCS states in terms of some entanglement measures.