Relaxation processes are studied for a two-level system which is placed under the influenced by a superposition of two environments. Two cases are treated: one is that the two-level system interacts with the environment via both linear dissipative coupling and pure dephasing coupling in the Markovian limit and the other uses an exactly solvable single-excitation spin-boson model. In both the cases, an ancillary two-level system determines which environment of the two actually interacts with the relevant two-level system. In the Markovian limit, the reduced time-evolution of the two-level system is characterized by the longitudinal relaxation time \(T_{1}\) and the transversal relaxation time \(T_{2}\) which satisfy the inequality \(2T_{1}\ge T_{2}\). If the strict inequality \(2T_{1}>T_{2}\) is fulfilled, the coherence of the two-level system can be definitely enhanced by the environmental superposition effect. If the equality \(2T_{1}=T_{2}\) holds, it can be improved probabilistically. On the other hand, in the exactly solvable model, although the non-Markovian effect is observed in the reduced time-evolution, the coherence can be improved only probabilistically since the model does not include a pure dephasing coupling.

研究了一个两层系统的松弛过程，该系统置于两个环境的叠加影响下。讨论了两种情况：一种是两级系统通过马尔可夫极限中的线性耗散耦合和纯相移耦合与环境相互作用，另一种是使用完全可解的单激发自旋玻色子模型。在这两种情况下，辅助两级系统都会确定两者中的哪个环境实际上与相关的两级系统交互。在马尔可夫极限中，两级系统的减小的时间演化的特征是满足不等式\（）的纵向弛豫时间\（T_ {1} \）和横向弛豫时间\（T_ {2} \）。 2T_ {1} \ ge T_ {2} \）。如果满足严格的不等式\（2T_ {1}> T_ {2} \），那么环境叠加效应肯定可以增强两级系统的相干性。如果等式\（2T_ {1} = T_ {2} \）成立，则可以概率上加以改善。另一方面，在完全可求解的模型中，尽管在减少的时间演化过程中观察到了非马尔可夫效应，但由于该模型不包括纯相移耦合，因此只能概率性地改善相干性。