Entanglement Detection Of W Class States

Entanglement is one of the non-classical properties of quantum mechanics,and plays a very important role in the research field of quantum information and quantum computing,such as quantum key distribution,quantum randomness verification,teleportation and superdense coding,etc.Therefore,it is necessary to study the entanglement detection of quantum states.So far,there have been studied on entanglement detection and entanglement sequential detection of bipartite states and part of tripartite states(maximal entangled W state and Greenberger-Horne-Zeilinger state),but there is no research on entanglement detection and entanglement sequential detection of extended tripartite states.In this dissertation,the entanglement detection of W class states is studied.The entanglement detection of the maximal entangled W-state and the asymmetrical W-state in the perfect W-state with the entanglement witness operator and Bell inequality is described.Because of the difficulties in preparing multiple entangled states,the study on preserving entanglement after several partial measurements is necessary.In this paper,we verify sequential entanglement detection of the tripartite asymmetrical W-state shared by Alice,Bob,and a sequence multiple Charlies.In order to witness genuine entanglement,we use an entanglement witness operator and the violations of two Bell-inequalities.Using the entanglement witness operator,we find that up to 3 Charlies can witness the entanglement of the system with a single Alice and a single Bob.We also find that the maximum number of Charlies can only reach 1 using the Mermin inequality and the Uffink inequality.