内禀退相干下光与原子相互作用系统的研究

【作者】 谭霞；

【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。 随着量子算法的提出和量子编码的实现,量子计算机的研究越来越受到人们的重视。量子计算利用了量子力学的本质特性——量子叠加性和相干性原理,来完成经典计算机所不能完成的大型计算,但是量子计算的实现还存在很大的困难,因为量子计算利用了量子力学中态的相干性,量子系统始终与环境存在耦合,不能将系统与环境完全隔离开来,要保持量子态的相干性并不容易,这一直是人们研究的课题之一。其中,Milburn提出了一个简单的内禀退相干模型,给出了对标准量子力学的简单修正。本文正是在此理论的基础上,通过求解系统的Milburn方程,研究了两能级原子与双模SU(1,1)相干态光场发生相互作用系统中,如下几个方面的问题: (1)研究了原子与场的纠缠及双模SU(1,1)相干态场的模间纠缠随时间的演化问题,讨论了内禀退相干、双模光子数差等对纠缠度的影响。结果表明,存在内禀退相干时,随着时间的演化,场一原子纠缠逐渐减小到一个确定值,而模间纠缠逐渐增大到一个确定值,两者演化的最终值只取决于双模光子数差和平均光子数,而与内禀退相干因子无关。 (2)分析了内禀退相干、双模光子数差和平均光子数对SU(1,1)相干态光场量子统计性质的影响。结果表明,内禀退相干增强了光场两模的聚束效应和模间相关程度,并使第一模始终处于亚泊松分布;存在内禀退相干时,场的二阶相干度仍具有明显的崩塌一回复现象,随着时间的演化,光场第一模处于亚泊松分布,光子呈现反聚束效应,光场两模间呈正相关,且为非经典相关,而在大部分时间区域,光场第二模处于泊松分布,光子呈现聚束效应:双模光子数差和平均光子数对量子统计性质也都有非常显著的影响。 (3)分析了内禀退相干、双模光子数差和平均光子数对原子布居数反转的影响。结果表明,双模光子数差不为零时,原子布居数反转具有明显的崩塌和回复现象;当平均光子数减小时,崩塌和回复现象将逐渐消失;存在内禀退相干时,仍存在崩塌和回复现象,但随着时间的演化,Rabi振荡的包更多还原

【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 is quantum state, 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 its classical counterpart.With the realization of quantum algorithm and the solution of error avoiding, quantum computing (QC) has attracted many scientists’ attention. Based on the properties of quantum superposition and coherence—the essence of quantum mechanics, quantum computing is intended to perform many difficult tasks, which cannot be solved by classical computers. However, as the quantum system is correlated with its external environment, it is very difficult to keep coherence of qubits, which is used in QC. Therefore, many people try to tackle this problem. For example, Milburn gave a simply model of intrinsic decoherence, and made a simply modification to the standard quantum mechanics. Based on this theory, we study some problems following by solving the Milburn equation exactly for the system of two-mode SU (1,1) coherence states and a two-level atom.(1) We investigate the time evolution of the entanglement of field-atom and one of two modes of field using the quantum-reduced entropy and quantum relative entropy, respectively. The influences of intrinsic decoherence and two-mode photon number difference on the evolution of the entanglement of field-atom and one of two modes of field has been discussed. The results show that the entanglement of field-atom reduced to a stationary value with time evolution and the entanglement between two modes increase to another stationary value with intrinsic decoherence, and the values only depend on the two-mode photon number and mean photon number.(2) The effects on the quantum statistical properties of the two-mode SU(1,1) coherent field induced by the intrinsic decoherence, the two-mode photon numberand the mean photon number are analyzed. The results show that the intrinsic decoherence strengthens the anti-bunching effect of the two-mode and the correlation intensity between the two modes and makes the first mode of the field always to be sub-Poissonian. The second-order coherence degree of the two-mode field also exhibits obvious collapse-revival effect with the intrinsic decoherence. The first mode of the field is sub-Poissonian with the evolution of the time. The photon anti-bunching appears and the correlation of the two modes of light is both positive and non-classical. But in most of the time, the second mode of the field is Poissonian with the evolution of the time and the photon bunching appears. The influences of the two- mode photon number and mean photon number on the quantum statistical properties are also very obvious.(3) The effects on the atomic population inversion induced by the intrinsic decoherence, the two-mode photon number and the mean photon number are analyzed. The results show that the collapse and revival phenomena of the atomic population inversion will appear when the two- mode photon number is not zero and will disappear gradually with the decrease of the mean photon number. The collapse and revival phenomena of the atomic population inversion will also appear with the intrinsic decoherence, but the amplitude of the Rabi oscillation will be reduced to zero with the evolution of the time.更多还原