Entanglement Dynamics Of Coupled Cavity QED Systems

With the development of computer science, the demand of the integration of chips has been stricter than that before, which results in the difficulties for the production and the processing of semiconductors. Under the pressure of the difficulties, we have to seek for a breakthrough in computer science. Obviously, we can achieve the purpose either by promoting the processing technique of semiconductors or by exploring for a new system which possesses the capacity for information processing. However, we seem to be trapped into trouble at promoting the processing technique of semiconductors, which compels us to choose the latter solution. After a struggling exploration for new systems, we finally discovered the quantum processors which are quite promising. And the quantum information science was born against such a background.Quantum entanglement is regarded as the foremost resource which is applied into many quantum techniques such as quantum teleportation, quantum cryptology and quantum computation. Nevertheless, some problems need to be resolved before we realize quantum information processing. Among the problems, the generation, maintenance and manipulation of quantum entangled states are the key points. Therefore, it is significant to study the evolution of quantum entanglement, as well as the maintenance and enhancement of entanglement. Cavity quantum electrodynamics is always considered as one of the ideal systems for quantum information processing. Thus, our study is based on a directly coupled cavity quantum electrodynamics system. We investigate the entanglement dynamics of two atoms which are trapped in the cavities under the cases that the fields are initially in vacuum states, separated state, entangled state and thermal states, respectively.The main contents are as follow:(1) We calculate the Negativities for the two atoms which are initially in maximally entangled state when the fields are initially in (â… ) maximally entangled state (|01>+|10>)1/2 and in (â…¡) separated state|10>, respectively. By means of numerical simulation, we find that the entanglement between the two atoms can maintain maximally entangled in both cases if the coupling strength of the cavities is large. When the coupling strength is small, compared with case (â…¡), the entanglement for the atoms only enhances at peaks instead of having a total improvement under case (â… ).(2) We take the dissipation of the atoms and the fields into account based on point (1). The numerical simulation indicates that the entanglement of the atoms have different sensitivities to the dissipation factors due to the different initial states of the fields.(3) We give the analytical solution of the Concurrence for the two atoms when the cavity fields are in the vacuum states. Furthermore, the entanglement dynamics of the two atoms interacting with two thermal fields which have symmetric mean photon numbers is investigated and the effective Hamiltonian is obtained in the case of large detuning. The numerical simulation illustrates that a larger coupling strength of the cavities is still advantageous to the entanglement of the atoms; on the contrary, the increase of the mean photon number is adverse to the entanglement of the atoms.(4) We consider the case that the two thermal fields have asymmetric mean photon numbers. By analyzing the numerical simulation of the Concurrence for the atoms, we find that the mean photon number affects the entanglement oscillation amplitudes heavily, but only have a small effect on the oscillation period.