腔QED中若干量子信息问题的研究

【作者】 单传家；

【导师】 夏云杰；

【作者基本信息】 曲阜师范大学 ， 理论物理， 2006， 硕士

【摘要】 量子信息学作为一门新兴学科,以量子计算机和量子通信为主要内容日益发展起来。量子信息学以量子位作为信息载体,按照量子力学原理进行计算或操作,从而使量子信息学比经典信息学更具有优越性。近几年来,量子信息在理论上和实验上都取得了重大的突破,创造出绝对安全的量子密钥、量子密集编码、量子隐形传态等经典信息理论不可思议的奇迹。量子通信是量子信息的一个重要的研究领域,目前主要涉及量子隐形传态、量子密集编码、量子密钥共享和量子秘密通信等方面。 腔QED主要思想是将俘获的原子约束在高品质腔中,把量子信息储存在原子能态上,囚禁的原子作为量子信息存储器,光腔用来进行量子信息的传输。随着腔QED实验的进展,腔QED方案就成为将来处理量子信息很有前途的理论方案。本论文主要研究了腔QED在量子信息中的应用,主要内容包括下面三部分: 1.研究了Tavis—Cummings模型中两纠缠原子纠缠的演化特性。我们研究了两个纠缠的两能级原子与单模粒子数场进行相互作用系统中两原子的纠缠演化,结果发现:两个原子之间的纠缠呈现出周期性的演化特性,初始两原子的状态、原子之间的偶极相互作用和粒子数场对腔中两个原子的纠缠有着显著的影响,并且还发现适当选择原子的初态,两原子会永远处于最大纠缠态。 2.研究了外场驱动下实现任意两原子未知态的隐形传态方案。在本论文中,我们实现了外场驱动下任意两原子未知态的隐形传态和受控的两原子未知态方案。在隐形传送的过程中,以两原子最大纠缠态作为量子通道,不用考虑腔场耗散和外界热场环境的影响,也不需要对原子进行Bell基测量,而且最终能成功实现传送的几率为1.0。 3.研究了外场驱动下实现量子密钥共享的方案。此方案利用原子而不是光子作为量子通道,可以一定程度上避免纠缠的退化。量子纠缠通道是开始就构建好的,在量子信息过程中,信息粒子不需要在通道中传输,可以保证通信的绝对安全。在这个方案中腔只是虚激发,因此腔场的退相干时间可更多还原

【Abstract】 Quantum information science, which mainly includes quantum computer and quantum communication, has increasingly evolved as a new object. Because the carrier of information in this subject, all the problems related to information should be resolved by means of quantum theory. Therefore, quantum information science exhibits a number of advantages corresponding to classical counterpart. In the past few years, quantum information has made a surprise progress both in theoretical and experimental fields, it has created many miracles, such as absolute secure quantum key, quantum dense coding, quantum teleportation, and so on. Quantum communication is an important branch of quantum information science, and mostly involves quantum teleportation, quantum dense coding, quantum secret share, quantum secure communication.The idea of the cavity QED is to trap several atoms in a small high quality optical cavity. Quantum information can again be stored in the internal states of the atoms. The trapped atoms will provide quantum memory and optical cavities will be utilized both to perform quantum gates and to transfer quantum information. With the experimental developments concerning cavity QED, electrodynamics (QED) technique has been proven to be a promising candidate for the physical realization of quantum information processing. In this thesis, we focus our research on the applications of cavity QED to quantum information. The main results of this thesis are as follows:1. The entanglement character of two entangled atoms in Tavis-Cummings model is investigated. We investigate the entanglement time evolution of two entangled two-level atoms that interact resonantly with a single-mode field in the Fock state. The results show that the two-atom entanglement state appears with periodicity. The influence of the two-atom initial state, the dipole- dipole coupling intensity between two atoms, and the field in the Fock state on the entanglement degree of two atoms are revealed. Meanwhile the two-atomquantum state will forever stay in the maximum entangled state when the initial state is proper.2. A scheme for the teleportation of an arbitrary two-atom state in driven cavity QED has been proposed. In this thesis, we studied the teleportation and controlled teleportation of an arbitrary two-atom state in driven cavity QED. In the teleportation, the maximally two-atom entangled state are required as the quantum channel, our scheme does not involve the Bell-state measurement and is insensitive to the cavity decay and the thermal field. The probability of the success in the teleportation is 1.0.3. A protocol for implementing quantum secret sharing via EPR states in driven cavity QED. The scheme utilizes entangled atoms instead of photons as the quantum channel, which avoids the entanglement decrease in a certain degree. Message particles are not transmitted in the quantum channel during the communication process, which ensures the absolute safety of the communication. In the scheme, the cavity is only virtually excited and thus the efficient decoherence time of the cavity is greatly prolonged. Moreover, the joint Bell-state measurement is not necessary in the cavity QED.更多还原