Ultracold metastable helium: from atoms to exotic molecules

We have written this article in the honor of our friend Vladilen Lethokov, who has produced so many brilliant ideas and results in the field of atomic and molecular physics and with whom we have had frequent unlightening discussions. We hope that the work described here will contribute to illustrate the richness of the field.     

Ultracold collisions in the system of three helium atoms

The Faddeev differential equations for a system of three particles with a hard-core interaction are described. Numerical results on the binding energies of the ⁴He₃ and ³He⁴He₂ trimers and on ultracold collisions of ^3,4He atoms with ⁴He₂ dimers obtained with the help of those differential equations are reviewed. The results obtained for the hard-core model using the Faddeev equations are compared with analogous results obtained by alternative methods.     

On dimers and trimers in some helium fluids

Some aspects of dimers and trimers are explored in a unified manner for various helium species. These include³He,⁴He and⁶He as well as combinations thereof. The subtle interplay among the central factors involved is delineated carefully. In particular, the dimer problem has been recast in three complementary forms which are based on: (1) the conventional eigenvalua equation in both its Schrödinger and Lippmann-Schwinger versions; (2) the quantum parameter; and (3) the concept of an eigenmass below which no binding occurs for a specific interatomic potential. This framework turns out to be adaptable, in its gross features, to two-dimensional systems and to the liquid phase as well. General implications ofn-merization in several helium liquids, comprising thin films, are examined briefly.Permanent address     

Heteronuclear and homonuclear high-spin alkali trimers on helium nanodroplets

The electronic excitation spectra of all possible homo- and heteronuclear high-spin (quartet) trimers of K and Rb (KxRb(3-x), x=0...3) assembled on the surface of superfluid helium droplets, are measured in the spectral range from 10,600 to 17,400 cm(-1). A regular series of corresponding bands is observed, reflecting the similar electronic structure of all these trimers. For the assignment and separation of overlapping bands, we determine x directly, with mass-selected beam depletion, and indirectly with a V-type double-resonance scheme. The assignment is confirmed by high-level ab initio calculations of the electronic structure of the bare trimers. The level structure is rationalized in terms of harmonic-oscillator states of the three valence electrons in a quantum-dot-like confining potential. We predict that three should be a magic number for high-spin alkali clusters.     

超冷中性等离子体的研究进展

超冷中性等离子体的产生对传统等离子体物理研究具有重要意义.文章介绍了超冷中性等离子体的研究进展,主要包括：超冷中性等离子体产生的物理机制和测量方法,超冷中性等离子体的扩散以及在扩散过程中里德伯原子的形成、电子温度的演化和各种加热冷却机制对扩散过程的影响,并对相关的理论模型作了概述.     

超冷中性等离子体的研究进展

超冷中性等离子体的产生对传统等离子体物理研究具有重要意义.文章介绍了超冷中性等离子体的研究进展,主要包括:超冷中性等离子体产生的物理机制和测量方法,超冷中性等离子体的扩散以及在扩散过程中里德伯原子的形成、电子温度的演化和各种加热冷却机制对扩散过程的影响,并对相关的理论模型作了概述.     

Ultracold electron source

We propose a technique for producing electron bunches that has the potential for advancing the state-of-the-art in brightness of pulsed electron sources by orders of magnitude. In addition, this method leads to femtosecond bunch lengths without the use of ultrafast lasers or magnetic compression. The electron source we propose is an ultracold plasma with electron temperatures down to 10 K, which can be fashioned from a cloud of laser-cooled atoms by photoionization just above threshold. Here we present results of simulations in a realistic setting, showing that an ultracold plasma has an enormous potential as a bright electron source.     

超冷极性分子

目前对超冷原子的研究已经从最初的原子分子物理扩展到了物理的很多分支.极性分子可以将电偶极相互作用引入到超冷体系,同时分子又与原子类似,可以灵活地被光和其他电磁场操控,因而很多理论工作都预言了超冷极性分子在超冷化学、量子模拟和量子信息等领域会有重要的应用.但由于超冷基态分子的制备非常困难,如何把超冷物理从原子发展到分子还是一个方兴未艾的课题.过去的10年间,各种分子冷却技术都取得了很大突破,本文回顾了这些进展,并着重介绍了基于异核冷原子的磁缔合结合受激拉曼转移这一技术,该技术在制备高密度的基态碱金属超冷极性分子上取得了较大的成功.本文也总结了超冷极性碱金属分子基本碰撞特性研究的一些实验结果.     

Ultracold Scattering and Universal Correlations

Particle-dimer scattering below and above the three-body threshold is studied using Faddeev differential equations. Correlations between the observables are shown and some analogies between three-nucleon and three-atom systems are discussed.     

超冷原子物理学与原子光学(续完)

3　原子光学激光冷却中性原子技术的发展成熟 ,不只是促进超冷原子物理学这个新的研究领域产生和发展起来 ,还同时推动了另一个新的研究领域———原子光学的形成和进步 .原子光学是原子物理学与光物理学的交叉新领域 .在这个新领域中 ,人们类似光物理中处理光 (光子 )那样来处理原子 .从物质粒子与光子在波粒二象性方面的对称地位 ,很容易理解出现相应的物质粒子光学的必然性 .实际上 ,电子光学已经存在了相当一段时间了 (由于发展电子显微镜技术 ) ,类似的研究还有离子光学 ,中子光学等 .上述意义下的原子光学研究 ,最早应该追溯到 1 92 9…     

Ultracold heteronuclear molecules and ferroelectric superfluids

We analyze the possibility of a ferroelectric transition in heteronuclear molecules consisting of Bose-Bose, Bose-Fermi, or Fermi-Fermi atom pairs. This transition is characterized by the appearance of a spontaneous electric polarization below a critical temperature. We discuss the existence of a ferroelectric Fermi liquid phase for Fermi molecules and the existence of a ferroelectric superfluid phase for Bose molecules characterized by the coexistence of ferroelectric and superfluid orders. Lastly, we propose an experiment to detect ferroelectric correlations through the observation of coherent dipole radiation pulses.     

Ultracold inelastic collisions in two dimensions

We show that cross sections for inelastic collisions of ultracold atoms or molecules confined by a harmonic potential have the same energy dependence as in pure 2D geometry. This indicates that chemical reactions and inelastic collisions may be suppressed in an ultracold gas under strong confinement in one dimension. We present a numerical proof of the threshold collision laws in 2D. Our results indicate that inelastic collisions in weak electromagnetic fields may be controlled by varying the orientation of the external field axis with respect to the plane of confinement.     

Ultracold plasma in blue-detuned optical molasses

The possibility of a new application of optical molasses for viscous confinement and control of the state of ultracold electron-ion neutral plasma containing ions with quantum transition resonant with respect to the laser radiation has been shown. This viscous confinement scheme is based on the action of radiation damping force upon plasma ions in the strong field of standing light wave with large positive (“blue”) frequency detuning from resonance.     

Quantum Optics of Ultracold Molecular Fields

We apply concepts of quantum optical coherence to characterize the coherent generation of a molecular field from a quantum-degenerate atomic sample, and discuss the impact of the quantum statistics of the atoms on that field. For atoms initially in a BEC the resulting molecular field is to a good approximation coherent. This is in sharp contrast to the case of atoms in a normal Fermi gas, where we can made use of an analogy with the Tavis-Cummings model to show that the statistics of the resulting molecular field is similar to that of a single-mode chaotic light field. The BCS case interpolates between the two extremes, with an ＇incoherent＇ contribution from unpaired atoms superposed to a ＇coherent＇ contribution from atomic Cooper pairs. We also comment on the temporal fluctuations characteristic of the formation of molecular dimers from ultracold fermionic atoms.     

Efimov Resonances in Ultracold Quantum Gases

Ultracold atomic gases have developed into prime systems for experimental studies of Efimov three-body physics and related few-body phenomena, which occur in the universal regime of resonant interactions. In the last few years, many important breakthroughs have been achieved, confirming basic predictions of universal few-body theory and deepening our understanding of such systems. We review the basic ideas along with the fast experimental developments of the field, focussing on ultracold cesium gases as a well-investigated model system. Triatomic Efimov resonances, atom-dimer Efimov resonances, and related four-body resonances are discussed as central observables. We also present some new observations of such resonances, supporting and complementing the set of available data.