原子的玻色-爱因斯坦凝聚

综述了玻色－－爱因斯坦凝聚（ＢＥＣ）实验研究工作的进展，介绍了玻色－爱因斯坦凝集的概念、形成条件和相关的实验技术，叙述了玻色－爱因斯坦凝集体（ＢＥＣ）和物理性质，展望了发展前景。     

玻色-爱因斯坦凝聚特性及其应用

本文介绍了北京大学建立的玻色-爱因斯坦凝聚实验平台，实现了玻色-爱因斯坦凝聚（图1），获得了原子数为五十万个，温度为50纳开尔文的玻色凝聚体。在此基础上我们精密测量了玻色-爱因斯坦凝聚的相变温度，还利用玻色-爱因斯坦凝聚实验平台通过马越让那跃迁获得了可控的多量子态玻色爱因斯坦凝聚体。并利用四种方法获得了原子激光（图2），其中有三种方法是国际上第一次使用。另外，我们提出了将玻色一爱因斯坦凝聚转入Magic光晶格阱，实现精度优于10^-17的新型原子钟的设想。     

超流^4He中玻色—爱因斯坦凝聚的直接证据

超流４Ｈｅ中玻色爱因斯坦凝聚的直接证据１９９７年度的诺贝尔物理学奖被授予朱棣文等三位科学家，以表彰他们在“激光冷却和捕获原子”方面的贡献．这项技术导致了中性碱金属原子的玻色－爱因斯坦凝聚（１９９５年），以及以凝聚为基础的位相相干Ｎａ原子束（俗称原子激...     

磁光捕获冷原子和玻色-爱因斯坦凝聚的研究进展

介绍了磁光捕获冷原子和玻色-爱因斯坦凝聚的物理特性及相关发展和研究,阐述了如何通过实验得到磁光捕获和玻色-爱因斯坦凝聚,并介绍了相关仪器,详细说明了测量其温度及捕获的原子数量的方法.同时还介绍了插入光和磁场上移等获得玻色-爱因斯坦凝聚的方法及红失谐和蓝失谐光如何捕获冷原子的研究.最后介绍了作者所做的研究:冷原子的快速压缩法和玻色-爱因斯坦凝聚的绝热捷径.     

从费米原子到配对超冷分子

自从1995年以来，实验物理学家已经在一系列玻色原子气系统中实现了玻色—爱因斯坦凝聚(BEC)，它们是^1H，^7Li，^23Na，^85Rb和^87Rb等等，这些玻色原子具有整数自旋量子数，与玻色原子相对应的是费米原子，它们具有半整数的自旋值，例如^40K。即使在非常接近绝对零度的低温下，费米原子气也不可能凝聚到单一量子态：每一个费米原子所     

玻色-爱因斯坦凝聚物理本质探索

针对玻色-爱因斯坦凝聚这一课题,综述了玻色-爱因斯坦凝聚理论的诞生和发展、概念,着重阐述了其形成条件、物理机制、性质及其应用,接着将介绍一些玻色—爱因斯坦凝聚的实验和国内外的研究动态,最后展望了其发展前景。     

2001年的诺贝尔物理奖

20 0 1年的诺贝尔物理奖颁发给了ＮＩＳＴ ＪＩＬＡ的Ｅ .Ｃｏｒｎｅｌｌ,ＭＩＴ的Ｗ .Ｋｅｔｔｅｒｌｅ和Ｃｏｌｏｒａｄａ ＪＩＬＡ的Ｃ .Ｗｉｅｍａｎ三位科学家 ,以表彰他们在玻色 -爱因斯坦凝聚方面的基础研究 .其中Ｅ .Ｃｏｒｎｅｌｌ和Ｃ .Ｗｉｅｍａｎ是首先考虑并实现在中性原子上的玻色 -爱因斯坦凝聚 (工作发表在Ｓｃｉｅｎｃｅ ,14Ｊｕｌｙ ,1995 ) ,随后Ｗ .Ｋｅｔｔｅｒｌｅ迅速做出了更大的玻色 -爱因斯坦凝聚 ,并扩展了对玻色 -爱因斯坦凝聚性质的研究 (工作发表于ＰｈｙｓｉｃａｌＲｅｖｉｅｗＬｅｔｔｅｒｓ ,2 7Ｎｏｖｅ…     

原子间相互作用对原子激光压缩性质的影响

研究了原子间相互作用对光场与原子玻色-爱因斯坦凝聚体相互作用系统中耦合输出的相干原子束压缩性质的影响．结果表明：原子激光的两正交分量的涨落均可压缩，玻色-爱因斯坦凝聚体中原子间的相互作用不利于原子激光的压缩． 关键词： 玻色-爱因斯坦凝聚 压缩相干态光场 压缩原子激光     

激光冷却及其在科学技术中的应用

这篇文章回顾了近20以来激光冷却原子气体的发展历史，同时概述了激光冷却的各种物理机制，还介绍了超冷原子物理在量子物理学和高科技应用中所取得的重要成就，包括气体原子的玻色-爱因斯坦凝聚、原子钟和原子干涉仪。     

超冷原子物理学与原子光学(续)

2 .2　超冷原子气体的玻色—爱因斯坦凝聚(ＢＥＣ)玻色—爱因斯坦凝聚是一种相变 ,其特点是宏观数量的粒子处于同一量子态 .有关这一物理现象的较详细的讨论 ,读者可参阅笔者有关的评述文章[16 ] .(1 )ＢＥＣ的提出和有关研究的历史发展1 92 4年印度的物理学家Ｓ .Ｎ .玻色在其论文“普朗克定律和光量子假说”中提出了一种新的统计方法 ,他将论文寄给了爱因斯坦 .爱因斯坦认识到该论文的重要意义 ,将其从英文译成德文并加上评注后寄给《物理学期刊》发表[17] .爱因斯坦接着在同年及次年初接连发表了二篇文章[18] (“单原子理想气体的量子理…     

光晶格中玻色-爱因斯坦凝聚体的自旋和磁研究

近年应用光晶格（optical lattice)控制原子玻色－爱因斯坦凝聚体（BEC）的研究取得了突破性的进展。德国Munich研究小组首次在三维光晶格中观察到了超冷原子从BEC超流状态向Mott insulator状态的量子相变。这样的量子相变现象不仅具有重大的理论研究价值，而且为BEC的实际应用提供了新的途径。文章介绍了作者近来在光晶格中BEC的自旋和磁特性方面的一些研究进展，并探讨了它们在磁传感器及量子计算中的可能应用。     

分子玻色凝聚体初露曙光

德州大学奥斯分校（University of Texas at Austin)的实验小组最近以受激拉曼跃迁的方法的将玻色－爱因斯坦凝聚体（Bose-Einstein condensate）中的铷原子转换为单一内部能态,温度约为100nK的铷分子（Rb2)^[1P。美国国家标准局（NIST）的资深物理学家Paul Julienne说,这可能是宇宙中最冷的分子。由于用传统的激光冷却的方式产生超冷分子有一定的难度,奥斯汀小组的实验为此另辟一条新种,并为分子凝聚体（molecular condensate）的诞生跨出了第一步。     

Transport behaviour of a Bose Einstein condensate in a bichromatic optical lattice

We investigate the Bloch and dipole oscillations of a Bose Einstein condensate (BEC) in an optical superlattice. We show that, as the effective mass increases in an optical superlattice, the BEC is localized in accordance with recent experimental observations [J.E. Lye et. al. Phys. Rev. A 75, 061603 (2007)]. In addition, we find that the secondary optical lattice is a useful additional tool to manipulate the dynamics of the atoms.      

Bose–Einstein condensation in the three-sphere and in the infinite slab: Analytical results

We study the finite size effects on Bose–Einstein condensation (BEC) of an ideal non-relativistic Bose gas in the three-sphere (spatial section of the Einstein universe) and in a partially finite box which is infinite in two of the spatial directions (infinite slab). Using the framework of grand-canonical statistics, we consider the number of particles, the condensate fraction and the specific heat. After obtaining asymptotic expansions for large system size, which are valid throughout the BEC regime, we describe analytically how the thermodynamic limit behaviour is approached. In particular, in the critical region of the BEC transition, we express the chemical potential and the specific heat as simple explicit functions of the temperature, highlighting the effects of finite size. These effects are seen to be different for the two different geometries. We also consider the Bose gas in a one-dimensional box, a system which does not possess BEC in the sense of a phase transition even in the infinite volume limit.     

Photon condensation: A new paradigm for Bose–Einstein condensation

Bose–Einstein condensation is a state of matter known to be responsible for peculiar properties exhibited by superfluid Helium-4 and superconductors. Bose–Einstein condensate (BEC) in its pure form is realizable with alkali atoms under ultra-cold temperatures. In this paper, we review the experimental scheme that demonstrates the atomic Bose–Einstein condensate. We also elaborate on the theoretical framework for atomic Bose–Einstein condensation, which includes statistical mechanics and the Gross–Pitaevskii equation. As an extension, we discuss Bose–Einstein condensation of photons realized in a fluorescent dye filled optical microcavity. We analyze this phenomenon based on the generalized Planck’s law in statistical mechanics. Further, a comparison is made between photon condensate and laser. We describe how photon condensate may be a possible alternative for lasers since it does not require an energy consuming population inversion process.     

The <Superscript>55</Superscript>Mn Spin Echo Test of Magnon BEC State in MnCO<Subscript>3</Subscript>

The coherent quantum state of magnons—Bose–Einstein condensate (BEC) has been observed in several types of antiferromagnets. According to the Bose statistics of magnons, BEC appears when the magnon density exceeds the critical density N _BEC and the magnon gas condenses to a quantum liquid. The BEC state is characterized by a coherent precession of the magnetization. In this paper, the first experiments showing the suppression of the spin echo signal by the magnon BEC is presented. These experiments confirm the coherence of magnetic excitations in the BEC state.     

On the Bose–Einstein Condensate of Excitons in Crystals with Defects

Optics and Spectroscopy - The possibility of formation of a Bose–Einstein condensate (BEC) of excitons in a model nonideal lattice of a molecular crystal is considered. The spectrum of...     

原子间相互作用对双模原子激光压缩性质的影响

研究了由单模压缩相干态光场与Ξ型三能级原子玻色爱因斯坦凝聚体(BEC)相互作用系统中耦合输出的双模原子激光的压缩特性,重点讨论了玻色爱因斯坦凝聚体原子间相互作用对原子激光压缩性质的影响,并讨论了原子激光压缩对光场初始压缩因子的依赖关系。结果表明:由光场诱导的双模原子激光呈现周期性的压缩,原子间的相互作用和光场初始压缩因子对原子的压缩性质具有重要影响。原子间的相互作用影响原子激光压缩的振荡频率而不会影响其压缩深度,而初始光场的压缩因子则对原子激光压缩深度产生调制作用,且初始光场的压缩因子越大,则原子激光压缩的时间越短。     

Nonadiabatic effects on population transfer of two Bose－Einstein condensates induced by atomic interaction

We investigate the stimulated Raman adiabatic passage for Bose－Einstein condensate (BEC) states which are trapped in different potential wells or two ground states of BEC in the same trap. We consider that lasers are nearly resonant with the atomic transitions. The difference of population transfer processes between BEC atoms and usual atoms is that the atomic interaction of the BEC atoms can cause some nonadiabatic effects, which may degrade the process. But with suitable detunings of laser pulses, the effects can be remedied to some extent according to different atomic interactions.     

Controlling Decoherence Speed Limit of a Single Impurity Atom in a Bose–Einstein‐Condensate Reservoir

The decoherence speed limit (DSL) of a single impurity atom immersed in a Bose‐Einstein‐condensed (BEC) reservoir when the impurity atom is in a double‐well potential is studied. It is demonstrated how the DSL of the impurity atom can be manipulated by engineering the BEC reservoir and the impurity potential within experimentally realistic limits. It is shown that the DSL can be controlled by changing key parameters such as the condensate scattering length, the effective dimension of the BEC reservoir, and the spatial configuration of the double‐well potential imposed on the impurity. The physical mechanisms of controlling the DSL at root of the spectral density of the BEC reservoir are uncovered.