The Entanglement Of Two Atoms In A Tavis-Cummings Model Driven By An External Field

Since 1990s, information science, which mainly includes quantum computer and quantum communication, has evolved as a new research field. Quantum entangled states, as a fundamental physical resource of quantum information processing, are extensively used in quantum computation and quantum communication, quantum teleportation, and quantum dense coding, etc. One of the key problems is the generation, measurement and manipulation of quantum entangled states in quantum systems.Tavis-Cummings model, which is based on Jaynes-Cummings model (a model for one two-level atom interacting with a single field) deals with the interaction between two identical two-level atoms and a single mode field. It can not only solve more complicated and realistic problems but also exist some precise results. It has both theoretical and experimental significance, so more attentions have been paid to it.In this thesis, we investigate the entanglement degree evolvement versus time of two atoms in a Tavis-Cummings model driven by an external field, it mainly includes four parts.The first part is preface, it introduces the development of quantum information, quantum entanglement and the model we discuss briefly.The second part is a simple review of basic theories of atom interacting with quantum field.In the third part, we introduce the entanglement theory, including the put forward of quantum entanglement, its definition, classification and measurement.In the fourth part, we borrow the entanglement degree measurement methods of Wootters and Peres to investigate the entanglement degree evolvement versus time of two atoms in a Tavis-Cummings model driven by an external field in the presence of dipole-dipole interaction. The results indicate: The coupling strength of two atoms can affect the changing speed of the entanglement degree; we can control the entanglement degree via modulating the strength of external field; when the strength of external field and the dipole-dipole interaction takes the appropriate value, the two atoms can be always entangled throughout experimental permiting time. These can be useful in quantum information processing. What's more, we find the two methods of entanglement degree measurement are equal in our system.