Study On The Fusion Of Entangled W States In Cavity QED

Quantum information science is a new interdiscipline of quantum mechanics and classical informatics,which is used to manage the quantum information based on the principles of quantum mechanics.Quantum entanglement is not only one of the most important physical concepts in quantum mechanics,but also a significant physical resource in quantum information processing.It is widely used in various fields of quantum information science.One can say that there is not the appearance of quantum information science without quantum entanglement.So,the study of quantum entangled states has extremely important scientific significance and value of application.In this thesis,we mainly study the preparation of entangled W states.For a special class of multi-particle entangled states,namely W states,it has a stronger quantum nonlocality and a better robustness to qubit loss than other multi-particle entangled states in quantum information processing(QIP)tasks.This means that it is very vital to study the preparation of such entangled states.Furthermore,because of imperfections of operation,the entangled W states actually available are all non-maximal ones.Studies suggest that there is a special class of non-maximally entangled W-like states,which can be used to achieve the perfect quantum teleportation and superdense coding.Therefore,the preparation of such W-like states is also an important research area in this thesis.Meanwhile,the inequivalent classes of multi-particle entangled states cannot be perfectly converted into each other by local operations and classical communication(LOCC),which is another important reason for studying W-state preparation separately.In this thesis,quantum state fusion technique is used to design the physical schemes for preparing the above two W states in cavity QED system.One is to fuse an N-atom W-like state and an M-atom W-like state,which is based on the large-detuning interaction between the atoms and the cavity mode,into an(M+N-1)-atom W-like state by detecting one atom which enters the fusion mechanism,and to fuse three W-like states of atomic numbers N,M and T into an(M+N+T-2)-atom W-like state.By calculations,the probability of success is fixed,i.e.,it does not depend on the initial number of atoms M,N and T.The other is that the fusion of two and three atomic W states would be realized without loss of atoms,based on the resonant interaction between atoms and cavity mode,by detecting the state of photon in the cavity mode.The analyses of the optimal resource cost and the experimental feasibility indicate that the present schemes are simpler and more efficient,and maybe implementable within the current experimental techniques.