Non-Markovian Dynamics And Weak Measurement Feedback Control Of Open Quantum Systems

Any realistic physical system will suffer from unwanted interactions with the out-side environments, causing decoherence and destroying entanglement. In order to in-vestigate the quantum decoherence and the entanglement dynamics of open quantum systems, we must take account of the characteristics of the environments coupled to the system. Usually, in the standard theory of the open quantum systems, environments are treated as the Markovian environments without memory. However, in the strong cou-pling regime, non-Markovian effects induced by the memory and feedback interactions of environments should be considered carefully. Recently, the strong coupling systems for quantum information processing has been realized with the development of science and technology. Thus, investigating the non-Markovian dynamics and related quantum feedback control of open quantum systems have important theoretical and partical sig-nificance. In this thesis, non-Markovian dynamics and weak measurement feedback control of open quantum systems have been studied by using the theories of open quan-tum systems and quantum information, and a series of significant results are obtained. The concrete contents are listed as follows:1. Based on the damped Jaynes-Cummings model, the entropy squeezing dynamics of a two-level atom off-resonantly coupled to a non-Markovian reservoir has been inves-tigated. The influences of non-Markovian effects and detunings on the atomic squeezing have been examined. It is interesting to note that atomic squeezing can be protected for a long time when both the non-Markovian effect and detuning are present simultaneously. The physical mechanism is that the decay rate is suppressed much more by detuning in the non-Markovian regime than in the Markovian case. These results provide a poten-tial method to extend the possible usage time of squeezing, which would be useful in high-precision applications. 2. We have studied the excited-state population dynamics of a three-level A-atom coupled to a non-Markovian reservoir. Comparing the Lorentzian time-dependent decay rate and population dynamics for the weak coupling regime with those for the strong coupling regime, we have noted that non-Markovian features exist in both regimes, but population dynamics shows fairly different behaviors since the non-Markovian effect can be neglected safely in weak coupling regime. The results have been interpreted from the perspective of information flow.3. We have presented two theoretical methods to protect the entanglement and quantum discord in non-Markovian regime:One is based on the technology of detuning control; the other is based on the classical driving fields acted upon the systems. The physical mechanism behind our results has been explained via the quasimode theory. Our schemes would be helpful for suppressing the decoherence and dis-entanglement by non-Markovian effect in practical quantum information processing.4. We have examined the use of weak measurement-based feedback control for stabilizing quantum states in the presence of different noise sources and with respect to different system states. We have found that the approach is sensitive to the system state, but for some suitable states, it works well for all typical types of noise sources. This scheme fairly balanced the trade-off between information gain and disturbance in quantum measurement, which might shed some new light on the achievement of optimal quantum feedback control.