Two-Mode Excited Entangled Coherent States And Their Entanglement Properties

As it is well known that quantum entanglement has been viewed as an essential resource for quantum information processing,and creating and manipulating of entangled states are essential for quantum information applications. Among these applications are quantum computation,quantum teleportation, and quantum cryptography.In recent years,much attention has been paid to continuous variable quantum information processing in which continuous-variable-type entangled pure states play a key role.For instance,two-state entangled coherent states are used to realize efficient quantum computation and quantum teleportation. Two-mode squeezed vacuum states have been applied to quantum dense coding.Therefore,it is an interesting topic to create and apply continuou-svariable-type entangled pure states.In this thesis,we propose the concept of two-mode excited entangled coherent states and study their entanglement properties.In the second chapter, we present a brief review about basic concepts of quantum entanglement and entanglement measures.In the third chapter,we review the basic theory about optical coherent states.In the forth chapter,we introduce the definition of two-mode excited entangled coherent states(TMEECSs)｜Ψ_±(α,m)>(m≠0)through acting two creation operators of a two-mode optical field on the two-mode entangled coherent states(ECSs).We obtain the coherent-state representation and the number-state representation of the TMEECSs,respectively.We propose a possible scheme to produce them from the two mode ECSs through an interaction between a two-level atom with a cavity field and quantum measurement technology.In the fifth chapter,we investigate entanglement characteristics of the TMEECSs｜Ψ_±(α,m,n)>(m,n≠0)and discuss the influence of photon excitations on quantum entanglement.It is found that the entanglement amount of the TMEECSs is generally larger that that of the single-mode excited entangled coherent states(SMEECSs)for the same photon excitation nomber.It is indicated that the TMEECS｜Ψ_+(α,m,n)> has quite different entanglement characters from the TMEECS｜Ψ_-(α,m,n)>.In the weak-field regime,photon excitations affect seriously entanglement of the TMEECS｜Ψ_+(α,m,n)> while the TMEECS｜Ψ_-(α,m,n)> is always a maximally entangled state.We also find that in the regime of the strong field and the lower excitation,the entanglement amount of the TMEECS｜Ψ_+(α,m,n)> enhances with the increase of the photon excitations,and decreases with the field strength.However,in the regime of the strong field and the higher excitation,the entanglement amount of the TMEECS｜Ψ_+(α,m,n)> decrease with the increase of the photon excitations, and enhances with the field strength.