利用相干态正交化(ECS)法,讨论了两量子比特Rabi模型中的纠缠动力学问题,选取量子比特初态为交换对称的贝尔态,选取光场初态为真空态,分析了不同跃迁频率和不同光场-量子比特耦合强度下量子比特的纠缠演化特性。研究结果表明,在弱耦合情况下,当两个全同的量子比特的跃迁频率与光场频率的差值相同时,纠缠演化几乎相同;当非全同的量子比特跃迁频率相对光场频率对称失谐时,纠缠度比全同时大,失谐量越大,纠缠越强,且纠缠的变化周期与失谐量成反比。在共振情况下,当耦合强度不相等时,两量子比特纠缠演化存在主极大与次极大交替出现的现象;保持其中一个量子比特与光场的耦合强度不变,另一量子比特的耦合强度越强,次极大的峰值越大,但主峰峰值始终能达到最大纠缠;整个过程中纠缠演化表现出周期性。

The entanglement dynamics in a two-qubit Rabi model is discussed by the extended coherent states (ECS) method. The two qubits are initially prepared in an exchange-symmetric Bell state and the initial state of the light field is the vacuum state. The entanglement evolution characteristics are analyzed under different transition frequencies of qubits and different coupling strengths between light fields and qubits. The results show that, in the case of weak coupling, when the differences between the transition frequencies of two identical qubits and the frequency of the light field are equal, the entanglement evolution is almost identical. When the transition frequencies of two non-identical qubits are symmetrically detuned relative to the frequency of the light field, the entanglement degree is larger than that for two identical qubits; the larger the detuning is, the stronger the entanglement is, and the entanglement evolution period has an inverse relationship with the detuning. Under the resonance conditions and when the coupling strengths are different, the phenomenon of the principal peaks and the secondary peaks appearing alternately in the entanglement evolution process of two qubits. If the coupling strength between one qubit and the light field is kept to be constant, the stronger the coupling strength of the other qubit is, the higher the secondary peaks become but, the principal peaks always reach the maximum entanglement. The entanglement evolves periodically in the whole process.