【作者】 王奕；

【导师】 叶柳；

【作者基本信息】 安徽大学 ， 原子与分子物理， 2012， 硕士

【摘要】 量子信息学自上世纪90年代初,逐步发展为一门新兴的热点学科,吸引了越来越多的科技工作者加入到这个研究队伍中。量子信息学根据应用对象的不同,可以分为量子计算和量子通信两部分,量子信息学的最终目标是：1.制造出真正意义上可实际应用的量子计算机；2.实现安全的实用的远程量子通信。目前,量子计算机的研究仍然处在理论研究阶段,而远程量子通信的研究已经开始开始从理论研究,进入应用研究。量子通信是一种全新的通信方式,它的主要研究内容有,量子隐形传态(不发送任何粒子而实现未知量子态的远程传送)、量子密集编码(通过传送一个量子比特而实现两比特信息的传输)等等,这些量子信息处理的过程归根结底是对量子纠缠态的制备和操作过程。目前,人们已经在多种系统中尝试量子信息研究,常见的物理系统有光学系统(Linear Optics)、腔动力学系统(Cavity QED)、离子阱系统(Ion Trap)、核磁共振系统(Nuclear Magnetic Resonance System)、量子点系统(Quantum Dot System)、低温超导系统等,这些系统的区别在于,使用不同的方式来储存信息。其中,光学系统是一种比较好的量子信息处理系统,它的实验进展也比较迅速。本文主要讨论多体纠缠态的制备和量子密集编码在线性光学系统中的实现过程。1.在光学系统中完成GHZ量子纠缠态的制备我们提出了一个在光学系统中,结合非线性交叉克尔效应,利用零拍探测,制备偏振三光子GHZ态的有效方案,而且这个方案可扩展用于制备N个光子的GHZ纠缠态,与其它系统中的方案相比,这个方案的优点是：制备成功率很高、保真度几乎接近100%。2.在光学系统中实现四粒子|Ψ)态的量子密集编码我们在光学系统中,利用简单的线性光学器件,首先提出一个对四粒子|Ψ>纠缠态进行一个粒子的密集编码方案,然后扩展到两个粒子的密集编码方案。在整个方案中,使用了非破坏性的奇偶校验探测器(PCD),该探测器同样使用零拍探测,利用信号光和探测光,在非线性交叉克尔介质中相互作用,对探测光相位改变的测量来实现,我们的密集编码方案成功的可能性接近于1。上述两个方案都在光子系统进行的,光子是中性粒子,它消相干时间比较长,所以,外界环境对光子纠缠态的影响比较小,不容易破坏光子态。在上述方案中使用的非线性交叉克尔效应,是在实验室中可以实现的,只要探测光场的强度足够大,那么,对交叉克尔效应强度的要求就不会很大。利用电磁感应透明(EIT-Electromagnetically induced transparency),在实验室中能获得这种强度的非线性交叉克尔效应强度。而采用了零拍探测,不仅避免探测对光子态的破坏,而且实验的可操作性也很强。在我们的方案中使用的各种线性光学元件,如PBS、BS、WP等,都是量子光学实验中常用的基本元件,在实验中利用这些线性光学元件,容易实现对光子的各种单比特操作,所以实验可行性较高。更多还原

【Abstract】 Since the early1990s, Quantum information gradually developed into an emerging hot spot disciplines, attracting a growing number of scientific and technological workers to join the research team. There are two branches, quantum computation and quantum communication, Their core objective are to create a true practical application of quantum computers and realize absolutely safe and practical quantum communication of long distance. Quantum computer is still in the phase of theoretical research, and distance quantum communication research has begun to gradually move from theory to experiment.Quantum communication is to deliver and process information based on quantum methods, its main contents are quantum teleportation (achieving the remote transmission of unknown quantum states while not sending any particles), quantum dense coding (transmitting two bits of information by sending a qubit). The process of quantum information processing in the final analysis is the process of preparation and operation of quantum entangled states.Currently, people have tried to study quantum information in a variety of systems, common physical systems have linear optics, cavity QED, the ion trap, nuclear magnetic resonance, quantum dots, low-temperature superconducting, etc., the difference of these systems is based on different information storage ways.The optical system is a good quantum information processing system, and the experimental development of the optical system is very quickly. This article focuses on preparation of multi-body entangled state and implementation process of quantum dense coding in the optical system.1. Preparation of the GHZ states in an optical system.We propose a scheme for preparation of polarized three-photon GHZ state in linear optics, combined with nonlinear cross-Kerr media and the use of homodyne detection, and this program can be extended for the preparation of N photon GHZ state, and compared to other schemes, the advantages of this scheme is a high probability of preparation, almost close to100%.2. Four-particle states of quantum dense coding in an optical system.In the linear optics, we use linear optical devices, proposing a four-particle entangled state dense coding scheme. Throughout the program, we use quantum non-demolition detector, this kind of detector also uses homodyne detection, the use of interaction by the signal mode and the detection mode, in the nonlinear cross-Kerr medium, the probe light phase-change measurements. The success probability of our dense coding scheme is close to1.These two schemes are belong to the linear optics, the photon is a neutral particle, it is relatively long decoherence time. Therefore, the external environment influence is relatively small, less likely to destroy the photon.Used in the above scenario the nonlinear cross-Kerr effect can be achieved in the laboratory, as long as the intensity of the probe light field is large enough, then the requirements of cross-Kerr effect intensity will not be great. The use of electromagnetically induced transparency, in the laboratory can obtain this strength of the nonlinear cross-Kerr effect intensity. Homodyne detection not only can avoid the single-photon detection destruction of the photon, and can also be feasible experimentally.Linear optical components used in our program, such as PBS, BS, the FS-PBS, etc., are commonly used in quantum optics experiments. It is easier to realize a variety of single-bit operations on the photon, so the experimental feasibility is very high.更多还原