| It is well-known that entangled states play the most important role in the study of quantum information. The importance is also shown in its application in quantum teleportation, quantum computation, quantum communication and quantum cryptography, and so on. In the actual quantum communication, the maximal entangled states are needed to transit the information. Therefore it becomes necessary to acquire the maximal entangled states from those whose entanglement is far away from the maximal entanglement. The process mentioned above is defined to be entanglement purification. It is clear that the process could be realized only through the interaction.In this thesis, the quantum electrodynamics (QED) technique is used to realize the process of purification. The basic dynamics of QED is first outlined, that is, the interaction between the atom with one cavity field. On the basis of atom-field interaction, two-atom purification and three-atom purification could be realized. The characteristic parameter for one purification method is the purification factor. In the study, we drew the purification factors from the time-dependent density matrix of the two-atom correlated system. The extremes of the factor could be gotten by differentiate the factors. The diagonal states of the density matrix are given, also the entanglement entropy of each state. The final goal of above discussion is evident to find the evolution time, to fulfill both diagonal states are maximally entangled and the purification factors are almost the extremes. |
