The Non-markovian Dynamics Of Several Open Quantum Systems

With the vigorous development of the quantum informationscience, quantum correlation has been viewed as an importantphysical resource in quantum information process. Any quantumsystem is interacting inevitably with its environment more or less,which leads to the quantum decoherence, making it difficult to dealwith quantum information efficiently. In the process of decoherence,different environments may lead to different dynamical results, so thecharacteristics of environments will have to be considered whenstudying the properties and behaviors of open quantum systems. Dueto the decoherence caused by environment will greatly reduce thecomputational efficiency even become invalid calculation, so in orderto enhance the quantum correlation, it is important to find a way toresist the quantum decoherence or extend the decoherence time.Based on the above reasons，in this dissertation,we studied thenon-Markovian dynamics of several open quantum systems andachieved some results. In Chap.1, the general situation of quantuminformation and the common knowledge of quantum dynamics hadbeen introduced, and the major organization of the dissertation isgiven at the end of this chapter. In Chap.2, we not only introduced thedecoherence, open quantum system, but also presented two kinds of quantum correlation including quantum entanglement and quantumdiscord. In Chap.3, the enhancement of quantum correlations bothfor quantum entanglement and quantum discord of two-level atoms ina single-mode cavity were studied. Furthermore, we discussed theinfluence of different parameters on two kinds of correlationenhancement. Then the enhancement parameter regions wereobtained by calculating the maximum and the average correlationswithin a certain time. What is more, we obtained that the region ofquantum discord enhancement is greater than that of quantumentanglement enhancement. Additionally, within a narrow range thequantum discord enhancement would increase as the temperaturerose, indicating that the quantum discord has more abilities to resistthe decoherence. In Chap.4, we studied the non-Markovianity ofHeisenberg XY model in a Fermi-thermal bath and combined it to thevolume of Bloch ball, finding that the non-Markovianty of quantumsystem interacting with the environment shown a fast decay with thetemperature and non-Markovian degree was much greater than1when beginning, indicating that the volume of the Bloch ballincreased more than once. We further calculated the situation thatwhen temperature is constant the non-Markovian degree wasincreasing with enhanced external magnetic field and shown a phasetransition point in time tends to spin chain of fast-growingenvironment trends.