极性分子系统中电磁诱导透明及量子开放系统中纠缠动力学研究
文献类型：学位论文
| 作者 | 周凤雪 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 龚尚庆 ; 张敬涛 |
| 关键词 | 极性分子，电磁诱导透明，四波混频，量子开放系统，量子纠缠 |
| 其他题名 | Studies on Electromagnetically Induced Transparency of Polar Molecule System and Entanglement Dynamics of Quantum Open System |
| 中文摘要 | 作为一种重要的量子干涉效应，电磁诱导透明是利用强相干光场诱导量子相消干涉，使介质对探测场的吸收和色散在共振点几乎降为零的现象。电磁诱导透明在众多领域中有着广泛的应用，例如，无反转激光放大、增强非线性、光学混频、量子信息的存储，等等。近年来，电磁诱导透明已经成为量子光学领域重要的前沿课题与研究热点之一，引起了人们的广泛关注。到目前为止，人们在各种材料介质中对电磁诱导透明现象从理论和实验两方面进行了深入的研究，从原子到分子，从气体到固体晶格，以及半导体量子点等等。但是，据我们所知，尚未有人在极性分子介质中对电磁诱导透明现象进行研究。所以，我们首次研究了极性分子系统中的电磁诱导透明及相关的非线性过程。 作为量子力学区别于经典力学的重要特征之一，量子纠缠不仅仅有利于对量子力学基本理论的理解，而且在量子信息领域，例如，量子稠密编码、量子密码、量子隐形传态等，扮演着极为重要的作用。但是在实际的量子信息处理中，量子纠缠体系不可避免地要受到周围环境的影响而产生退相干和信息丢失，所以实现量子信息和量子计算必须要克服这一难题。对量子退相干问题的研究是量子控制的前提，因此探讨开放系统的量子退相干以及量子纠缠动力学行为成为了近年来人们关注的一个焦点。另外，量子点中的电子自旋是实现量子信息单元–量子比特–的优秀的备选材料之一，针对量子点中电子自旋量子比特的纠缠动力学研究对于未来半导体材料中量子信息过程的实现具有重要的参考价值。 本论文主要就极性分子系统中的电磁诱导透明及相关的非线性过程、量子点中电子自旋量子比特的纠缠动力学进行了研究，所取得的主要研究成果如下： 研究了基于 HCN→HNC 异质结构的三能级 Λ 型极性分子系统中的电磁诱导透明现象。结果表明：固有偶极矩的存在导致了不同于一般的原子和非极性分子系统的现象。在 (1+1) 单光子跃迁过程中，因为限制了耦合场的拉比频率，固有偶极矩对于电磁诱导透明现象起到消极作用。但是，在 (2+2) 双光子跃迁过程中，固有偶极矩的存在，可以产生电磁诱导透明和无反转增益现象，并可以通过调控固有偶极矩系数来实现电磁诱导透明和无反转增益这两种过程的转换，进而实现慢光和快光过程的转换。 以电磁诱导透明为基础，研究了极性分子系统中的双光子共振非简并四波混频过程，分析了固有偶极矩对非线性四波混频转换效率的影响。结果表明：双光子跃迁能级间的固有偶极矩差越大，三阶非线性极化率越强，有利于增强生成信号场强度，进而提高四波混频转换效率。 研究了在非均匀外磁场作用下，耦合量子点中两个电子自旋量子比特模型的纠缠动力学问题。在两类不同的 X 型初始态下，详细分析了各个主要的参数对系统纠缠度演化的影响：包括外磁场强度和非均匀度、电子自旋之间的海森堡相互作用、电子自旋与晶格自旋库的耦合强度等参数对纠缠度的影响。结果表明：在纠缠演化过程中，非均匀外磁场所起的作用与系统初始态密切相关。对于初始为最大纠缠的贝尔态时，外磁场可以增强系统纠缠恢复的强度；对于初始为非纠缠态时，外磁场起负作用，削弱了系统生成的纠缠度；初始为对称的 α 态时，均匀磁场对纠缠演化没有影响。对非对称的 α 态，提高平均磁场强度可以减小纠缠衰减的幅度。适当提高外磁场的非均匀度，可以抑制自旋-轨道耦合的退相干和晶格自旋库的退相干作用，进而提高系统的纠缠度。 |
| 英文摘要 | Electromagnetically induced transparency (EIT) is an important quantum interference effect, which renders an optically thick medium transparent for a weak laser radiation over a narrow spectral range within an absorption line by inducing destructive coherence of atom states via a strong coherent optical field. Recently, the study of EIT that gains considerable interest has become an important frontier and a hot research topic in quantum optics, due to its wide applications, such as laser without inversion, enhanced optical nonlinearity, frequency mixing processes, information storage, etc. In the past decades, great efforts have been made in this area and there have been a large number of theoretical contributions and experimental demonstrations of EIT in atomic and molecular gases, ion-doped crystals, semiconductors, and superconducting quantum devices. Still, as far as we know, EIT in polar molecules has not been studied. Quantum entanglement is one of the most intriguing characteristics of quantum mechanics, it not only can lead to a deeper understanding of the foundation of quantum mechanics, but also can play an essential role in quantum information processing, such as, quantum cryptography, quantum dense coding, and quantum teleportation, etc. However, it is inevitable that the realistic quantum entangled system is coupled to the environment which causes decoherence and loss of information. In order to realize a useful quantum task in quantum information and quantum computation, it is necessary to be able to combat decoherence. Therefore, researches on quantum decoherence and entanglement recently come to be a focus of attention. Here, we are interested in electron spin in quantum dot which is one of the most promising candidates for qubit in various quantum information processing, and the research on the entanglement dynamics of coupled electron spin qubits in quantum dots might be valuable for the realization of quantum information processing in semiconductor. In this thesis, we investigate the EIT and its related nonlinear optical phenomena in polar molecules, the entanglement dynamics of two electron spins in quantum dots. The main results of this thesis are listed as follows: EIT in a three-level $\Lambda$-type molecular system with nonzero permanent dipole moments is investigated. It is shown that in the (2+2)-transition processes, when the sign of $d_{21}$, the difference in permanent dipole moments of the probe transition, is positive, perfect electromagnetically induced transparency with steep normal dispersion could be obtained under specific conditions. In contrast, when the sign of $d_{21}$ is negative, surprisingly gain without inversion with steep anomalous dispersion could be attained. The two-photon resonance four-wave mixing process based on EIT in the polar molecules is investigated. The effect of the permanent-dipole moments of polar media on the two-photon resonance four-wave mixing process is analyzed. It is demonstrated that the third-order nonlinear susceptibility of the medium is proportional to the difference in permanent dipole moments of the two-photon transition, and enhanced four-wave mixing conversion efficiency is obtained. The entanglement dynamics of two electronic spin in coupled quantum dots under a non-uniform field is investigated. The effects off the non-uniform magnetic field is discussed in detail for two kinds of X-type initial states, extended Werner like (EWL) states and $\alpha$ states. It is shown that the role of the field serves in the entanglement dynamics of the system is very sensitive to the initial state of system. Entanglement revival can be enhanced by the field when the initial states of system are Bell states while entanglement generation induced by the interaction between the electron spins is decayed by the field when the initial states are un-entangled states. For the symmetry $\alpha$ states, uniform field will not play a role on the dynamics while for the asymmetry $\alpha$ states, the amplitude of entanglement decay will be depressed by the uniform field. The inhomogeneity of the field can enhance the entanglement by suppressing the decoherence caused by the spin-orbit interaction and the spin bath. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15668]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 周凤雪. 极性分子系统中电磁诱导透明及量子开放系统中纠缠动力学研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。