SPECTRUM OF THE MICROMASER INJECTED WITH Λ-TYPE THREE-LEVEL ATOMS

The spectrum of the micromaser injected with A-type three-level atoms is studied. The spectrum has a Lorentzian lineshape and its central frequency has a shift. The effects of various parameters (for example, the atomic center-of-maas velocity, the cavity-length, the one-photon detuning, the ratio of the atomic injection rate to the cavity decay rate and the number of thermal photons) on the linewidth and the frequency shift are examined. The spectrum shows very different features in different velocity regimes, i.e., in the fast-atom regime, in the intermediate-velocity-atom regime, and in the slow-atom regime.     

One-step implementation of an N-qubit quantum phase gate through a double Raman passage

We propose a scheme for controllably implementing an N-qubit phase gate by one step within a ground-state subspace of N three-state atoms trapped in a cavity through a double Raman passage.We can extend our scheme to the realisation of an arbitrary N-qubit phase gate by appropriately adjusting coupling strengths and detunings between atoms and external driving fields.The advantage of this one-step scheme is its robustness against decoherence.     

Schemes for Generating Cluster States via Cavity Systems

We propose a scheme for generating an N-atom cluster state via cavity quantum electrodynamics （ CQED）. In our scheme, there is no transfer of quantum information between the atoms and the cavity, i.e., the cavity is always in the vacuum state, so the cavity decay can be suppressed. Also, the generated cluster state is the entanglement of the ground states, so the atomic spontaneous emission can be avoided. Therefore, the cluster state generated in our scheme has a longer lifetime. Furthermore, the requirement on the quality factor of the cavity greatly loosened for the cavity is only virtually excited.     

New approach for normalization and photon-number distributions of photon-added （-subtracted） squeezed thermal states

Using the thermal field dynamics theory to convert the thermal state into a "pure" state in doubled Fock space, we find that the average value of efa a under squeezed thermal state (STS) is just the generating function of Legendre polynomials. Based on this remarkable result, the normalization and photon-number distributions of m-photon added (or subtracted) STSs are conviently obtained as the Legendre polynomials. This new concise method can be expanded to the entangled case.     

单原子操控——2012年诺贝尔物理学奖得主Haroche科学成就简介

2012年诺贝尔物理学奖授予了法国的Serge Haroche和美国的David J.Wineland,以表彰他们在单粒子(单原子或单离子)操控领域的杰出贡献.他们两人分别参与开创了单粒子操控的两类实验系统,并利用这些实验系统研究了许多有意义的物理效应.简单来说,Haroche的实验系统研究飞行原子与光场的相互作用;Wineland的实验系统研究囚禁离子与光场的相互作用.本文简要介绍Haroche小组的工作.     

两模腔中的参量上转换和下转换

提出了一种通过建立双线性二次哈密顿量在量子腔中实现参量上转换和下转换的方案.通常在非线性过程中,介质本身不参与能量的净交换,但光波频率可以发生转换的作用称为参量转换作用.此方案建立在一个四能级原子同时与两经典场和两量子场相互作用的基础上,理论属于非线性光学四波混频范畴.将原子制备在合适的能级上,经典光场与相应的能级发生共振,而同时量子光场与相应的能级产生大失谐相互作用,在强相互作用区域内,原子和腔场失耦合,进而实现腔模的参量转换.根据所制备初始能级的不同以及光场激发能级的差异,分别实现了参量上转换和参量下转换.在利用参量下转换制备压缩算符后,对实验的可行性进行了讨论,并且给出了理论值.结果表明：在级联三能原子中采用一个级联双光子过程代替了原来的两个偶极禁戒跃迁间的经典驱动,可以保证高的不同频率之间的转换效率,并且用于光的量子操控和量子信息处理.     

连续CO2激光脉冲制作长周期光纤光栅的研究

利用耦合模理论分析了均匀长周期光纤光栅中的模式耦合, 描述了连续CO₂激光脉冲逐点写入长周期光纤光栅技术的实验研究情况, 实验中观测到模式耦合强度随光栅区域长度发生周期性变化.     

Entanglement of two two-level atoms trapped in coupled cavities with a Kerr medium

In this paper, the entanglement dynamics of two two-level atoms trapped in coupled cavities with a Kerr medium is investigated, We find that the phenomena of entanglement sudden death （ESD） and entanglement sudden birth （ESB） appear during the evolution process. The influences of initial atomic states, Kerr medium, and cavity-cavity hopping rate on the atom-atom entanglement are discussed. The results obtained by the numerical method show that the atom- atom entanglement is strengthened and even prevented from ESD with increasing cavity-cavity hopping rate and Kerr nonlinearity.     

Adjustable quantum coherence effects in a hybrid optomechanical system

We propose a system for achieving some adjustable quantum coherence effects, including the normal-mode splitting(NMS), the optomechanically induced transparency(OMIT), and the optomechanically induced absorption(OMIA). In this system, two tunnel-coupled optomechanical cavities are each driven by a coupling field and coupled to an atomic ensemble.Besides, one of the cavities is also injected with a probe field. When the system works under different conditions, we can obtain the NMS, the OMIT, and the OMIA, respectively. These effects can be flexibly adjusted by the tunnel coupling between the two cavities, the power of the coupling lasers, and the coupling strength between the atomic ensembles and the cavity fields. Furthermore, we can realize the OMIT even if the oscillating mirrors have relatively larger decay rates.     

Kerr介质中耦合双原子的纠缠特性

研究了Kerr介质中两个耦合二能级原子的纠缠演化规律, 通过concurrence计算了系统的纠缠度, 讨论了系统初态、Kerr 介质和原子之间的偶极相互作用对腔中两个原子纠缠度的影响. 结果表明: 通过适当选取Kerr介质的耦合系数和偶极相互作用强度, 可以获得固定的两原子纠缠, 并且可以提高两原子之间的纠缠, 甚至彻底消除纠缠猝死现象. 关键词： 偶极相互作用 Kerr介质 concurrence