Single-atom manipulations in a microscopic dipole trap

We have realized a very small optical dipole trap that is designed to store and manipulate individual atoms. Due to the very small dipole-trap volume, a 'collisional blockade' mechanism locks the average number of trapped atoms at a value of 0.5 over a large range of loading rates. Here we describe methods to characterize the motion of a single trapped atom, and we also demonstrate the possibility of trapping two atoms individually at a short distance apart. Finally, we study theoretically the possibility to perform 'conditional quantum logic' by scattering photons from two such atoms.     

Optical Observation of Atomic Hydrogen on the Surface of Liquid Helium

We have optically detected hydrogen atoms adsorbed on the surface of liquid helium, a system relevant for the study of Base degeneracy in two dimensions. The atoms are excited by 121.6 nm light and detected both in fluorescence and in absorption. The optical spectrum of the adsorbed hydrogen atoms was not known a priori. It shows a resonance that is much broader than that of a hydrogen atom in vacuo, and it is shifted to lower frequencies. From the fluorescence intensity we determine that we have reached a surface density corresponding to one atom per square De Broglie wavelength. This means that our experiments take place at the edge of quantum degeneracy. In the regime where the adsorption isotherm is known we can use the measured hydrogen densities to infer the temperature of the helium surface. We use this information to determine the thermal conductance between the surface and the bulk of liquid helium. We find quantitative agreement between the measured temperature drops and the prediction of ripplon-phonon coupling theory.     

How to catch an atom with single photons

Abstract

We report on trapping a single neutral atom in the standing-wave light field of a high-finesse optical cavity containing one photon on average, a single-photon optical trap, or SPOT for short. This trap has the novel feature that the light field is also used to observe the atom in real time. The oscillatory motion of the trapped atom induces well-resolved oscillations of the light intensity. Periodic structure is visible in the fourth-order intensity correlation function, attributed to long-distance flights of the atom along the standing wave. The finite duration of those flights provides evidence for cavity-mediated cooling of atoms. We discuss the various mechanisms determining the trapping time and compare the results with a quantum-jump Monte Carlo simulation to interpret the observed signals.     

Atom guiding along high order Laguerre–Gaussian light beams formed by spatial light modulation

A spatial light modulator (SLM) has been used to create high quality Laguerre–Gaussian (LG) light beams, which have been used to study the guiding of cold rubidium atoms. The SLM allows real-time variation of the hollow guiding beam and permits direct comparison of the guided atom fluxes for different LG modes with minimal adjustment of the other optical components. It is demonstrated that, by increasing the azimuthal index l of the Laguerre–Gaussian beam, the radiation pressure pushing the trapped atoms may be reduced while maintaining the same guided flux. This is the first comparative study of hollow beam atom guiding, and further demonstrates the versatility of the SLM for studies in atom optics.     

Preparation of two-mode anticorrelated photon-number state via atom de Broglie wave deflection

Abstract

It is shown that the deflection of an atom de Broglie wave at two adjacent cavities containing non-resonant weak fields can yield a highly entangled quantum state of the atom–field system in which discernible atomic beams are entangled to internal states of the atom and to two-mode photon-number states of the fields. Two-mode anticorrelated entangled photon-number states characterized by the total photon number can be prepared by the detection of the atom in given directions of the propagation.     

柱锥体环形切割器壳体飞散仿真研究

为研究串联战斗部前级装药对后级随进战斗部的影响,验证在现有导弹战斗部前端加装环形聚能装药的可行性,利用ANSYS/LS-DYNA软件进行了柱锥体环形切割器壳体飞散的数值仿真,得到了在其后级随进战斗部之前的空气域中的飞散路径,获得了这部分空气域内的爆炸响应冲击波的时间-压力历程。仿真结果表明,柱锥体环形切割器壳体破裂后,以壳体端部和壳体内侧上部对后级随进战斗部的影响为主,而内侧上部壳体受爆轰波影响形成聚能侵彻体对后级随进战斗部的影响最大,这为串联战斗部中对后级随进战斗部的隔爆设计打下了基础。     

柱锥体环形切割器壳体飞散仿真研究

为研究串联战斗部前级装药对后级随进战斗部的影响,验证在现有导弹战斗部前端加装环形聚能装药的可行性,利用ANSYS/LS-DYNA软件进行了柱锥体环形切割器壳体飞散的数值仿真,得到了在其后级随进战斗部之前的空气域中的飞散路径,获得了这部分空气域内的爆炸响应冲击波的时间-压力历程。仿真结果表明,柱锥体环形切割器壳体破裂后,以壳体端部和壳体内侧上部对后级随进战斗部的影响为主,而内侧上部壳体受爆轰波影响形成聚能侵彻体对后级随进战斗部的影响最大,这为串联战斗部中对后级随进战斗部的隔爆设计打下了基础。     

Generation of adjustable partially coherent bottle beams by use of an axicon-lens system

We report, what is to our knowledge, the first experimental realization of partially coherent bottle beams. It is shown that partially coherent bottle beams can be achieved by the focusing of partially coherent light with an axicon-lens system. The influence of the spatial coherence of the incident partially coherent light and other parameters, such as the radius of the limiting aperture of the axicon and the distance between the axicon and the lens, on the size of the bottle beams is investigated. We find that the longer the spatial coherence length, the larger the size of the resultant bottle beams. This dependence of the size of the bottle beams on the spatial coherence of the incident light provides a facile approach for generating adjustable partially coherent bottle beams. This kind of partially coherent bottle beam may have applications in atom optics, such as in atom trapping and atom guiding, etc.     

Optics for Neutral Atomic Beams: Reflection and Diffraction of Sodium Atoms by Evanescent Laser Light Fields

Abstract

Realization of the analogues of optical components for the manipulation of atomic de Broglie waves has recently become possible through the use of laser-based techniques. The strong fields generated by laser light have already been used to reflect atoms using travelling evanescent waves, and to diffract atomic beams through small angles using transmission gratings formed by a standing laser light wave in vacuo. Present experiments aim to combine these techniques to produce a reflection diffraction grating formed by a standing evanescent laser-light field, and to exploit the larger diffraction angles made possible theoretically by such a scheme.     

Polariton parametric amplification in semiconductor microcavities

Modifying the photonic environment of a semiconductor quantum well by embedding it in a high-reflectivity microcavity gives rise to new fundamental optical excitations, half-quantum well excitons, half-photons. These particles, called polaritons, have a light mass, as cavity photons, meaning that they have a large De Broglie wavelength. On the other hand, polaritons, like excitons, are subject to Coulomb interaction, a feature generating strong optical nonlinearities. Such properties favour quantum degeneracy and collective phenomena related to the bosonic statistics of polaritons. We review experiments on stimulated scattering of polaritons. In particular we concentrate on the resonant excitation of polaritons somewhere on the dispersion curve and the stimulation of their scattering into the fundamental state by means of an optical probe beam. The process is called polariton parametric amplification and results in very large and ultrafast optical amplification of the probe beam. The model, based on a Hamiltonian of interacting bosons, suggests that the amplification is related to the coherence between polaritons. We demonstrate that in clearly designed samples, this coherence can be preserved almost up to room temperature, so that intersting applications of this phenomenon can be conceived. At the same time we have been able to improve dramatically the efficiency of the parametric process, making the microcavity an unprecedented optical amplifier.     

Optical frequency standard based on cold Ca atoms

An optical frequency standard (/spl lambda/=657 nm) based on cold neutral Ca atoms released from a magnetooptical trap has been realized. Systematic contributions to the uncertainty resulting from the residual velocity of the atoms and the acceleration in the gravitational field are determined and reduced by using a combination of different atom interferometers. With the uncertainty for the effect of cold collisions reduced and an AC Stark shift eliminated, the relative uncertainty in the measured frequency of the Ca clock transition is reduced to 2/spl times/10/sup -14/. The application of a novel method for producing ultracold atoms showed the potential to further reduce the relative uncertainty to below 10/sup -15/.     

1K～100K温区He-3低温热物性数据计算

由于量子效应的影响，低温下He-3的性质与He-4有很大差异，对于4K－20K气相He-3的性质可利用改进的Strobridge方程来计算，而在20K－100K温区，通过引入对比德布罗意波长作为第三参数来描述量子效应而建立的改进量子对比态模型可用于计算该温区He-3的性质，基于上述计算方法，采用计算机程序设计，建立了He-3低温热物性数据库，该数据库可以计算压力在10MPa以下，温度介于1K－100K之间He-3的pVT性质，焓、内能、熵，热导率和粘度，其计算精度基本可以满足工程需要。     

The enhancement of spontaneous and induced transition rates by a Bose-Einstein condensate

Abstract

In this paper, an exactly solved model for the emission by N atoms is presented, the spontaneous and induced transition rates obtained, are enhanced by a factor which is proportional to the number of atoms n in the volume Λ³(2π²) (A is the transition wavelength of the atom) and dependent on the de-Broglie wavelength Λ_B in a more complicated way.     

Realization of a mirror magneto-optical trap

Abstract

We present details for construction and the operation of a mirror magneto-optical trap for cooling and trapping rubidium atoms. For trap operation, only four input laser beams are needed in contrast to the normal six for a standard trap. In excess of 10⁸ atoms have been trapped with this arrangement, with the atomic ensemble only ～1mm from the surface of a reflective mirror. This trap is highly suited to studies of magnetic guiding and magnetic manipulation of cold atomic ensembles.     

Non-linear processes in the interaction of atoms and molecules with intense EUV and X-ray fields from SASE free electron lasers (FELs)

The advent of free electron laser (FEL) facilities capable of delivering high intensity pulses in the extreme-UV to X-ray spectral range has opened up a wide vista of opportunities to study and control light matter interactions in hitherto unexplored parameter regimes. In particular, current short wavelength FELs can uniquely drive non-linear processes mediated by inner shell electrons and in fields where the photon energy can be as high as 10 keV and so the corresponding optical period reaches below one attosecond. Combined with ultrafast optical lasers, or simply employing wavefront division, pump probe experiments can be performed with femtosecond time resolution. As single photon ionization of atoms and molecules is by now very well understood, they provide the ideal targets for early experiments by which not only FELs can be characterised and benchmarked but can also be the natural departure point in the hunt for non-linear behaviour of atomistic systems bathed in laser fields of ultrahigh photon energy. In this topical review we illustrate with specific examples the gamut of apposite experiments in atomic, molecular physics currently underway at the SCSS Test Accelerator (Japan), FLASH (Hamburg) and LCLS (Stanford).     

Calculation of Charge Carrier Concentration Profile in a Wide Potential Well with Electric and Magnetic Fields

We investigated an equilibrium state of Fermi electrons in modulation doped structures with a wide quantum well in a strong parallel magnetic field. We studied the charge carrier system with a sufficiently high density, such that the de Broglie wavelength of electrons is smaller than the potential well width. We have formulated hydrodynamic equations for this carrier system both in the absence of magnetic field and in a parallel magnetic field. We have obtained analytical solutions for the charge carrier concentration as a function of coordinates in the potential well. In a quantum area near the interface, we carried out quantum mechanical calculations taking into account the effect of electric and magnetic fields. The concentration profile is presented for modulation doped Si/SiGe/Si heterostructures. We discuss large positive magnetoresistance in a strong parallel magnetic field in these structures.     

Magnetostatic analog for the calculation of phase contours inelectron holography of magnetic films

A method is presented for predicting the electron holographic interference pattern from a given magnetization distribution, and it is explained how phase contours can be sketched using magnetostatic intuition. The presented method is derived from the classical Lorentz force and the de Broglie relation between momentum and wavelength. The calculation of the electron phase to a two-dimensional magnetostatics problem is also mapped to which engineering experience and familiar mathematical methods can be applied. The result is considered simple to state and to remember     

Stress intensity factors for crack tip shielding or anti-shielding by impurity atoms

The average value of the crack tip stress intensity factor produced by a row of impurity atoms is calculated in this paper. The row of impurity atoms lies parallel to the crack front and is situated at an arbitrary position about a crack. The impurity atom produced mode I shielding/antishielding stress intensity factor L _iI for a row of impurity atoms very close to the crack tip is given by the expression: 295-1 where 2a is the crack length, a ^* is either the atomic radius of the host atoms (for substitutional impurities) or the radius of the vacant interstitial site (for interstitial impurities), 295-2 and 295-3 where G is the shear modulus, c is the fraction of impurity atoms in the impurity atom row and is the misfit parameter of the impurity atoms, r ₂ is the distance from the crack tip, and 295-4 is the angle the radius r ₂ makes with the crack plane.

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Résumé On calcule dans ce travail la valeur moyenne du facteur d'intensité de contraintes occasionné par une rangée d'atomes étrangers, située parallèlement à un front the fissure, et en une position arbitraire par rapport à la fissure.L'atome intersticiel ou de substitution génère une facteur d'intensité de contrainte de mode I, qui interfère sur une rangée d'atomes étrangers très proche de l'extrémité de la fissure, selon une expression ou interviennent la longueur de la fissure, le rayon atomique des atomes donnant lieu à une substitution ou à une insertion d'atomes étrangers, le module de cisaillement, la fraction d'atomes étrangers présents sur une rangée, le paramètre de désaxement des atomes étrangers, la distance de la rangée par rapport à l'extrémité de la fissure, et l'angle qui caractérise cette distance par rapport au plan de la fissure.

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This research has been performed under the auspices of the U.S. Department of Energy.     

Entanglement sudden birth and sudden death in a system of two distant atoms coupled via an optical element

An investigation is reported of the collective effects and the dynamics of atom–atom entanglement in a system of two distant two-level atoms which are coupled via an optical element. In the system under consideration, the two atoms, which are trapped in the foci of a lens, are coupled to a common environment being in the vacuum state and they emit photons spontaneously. A fraction of the emitted photons from each atom is thus focused on the position of the other atom. The presence of optical element between two distant atoms leads to the occurrence of delayed collective effects, such as delayed dipole–dipole interaction and delayed collective spontaneous emission, which play the crucial role in the dynamical behaviour of the entanglement. We discuss the phenomena of entanglement sudden birth, entanglement sudden death, and revival of entanglement for both cases of initial one-photon and initial two-photon unentangled atomic states. We show that the evolution of the entanglement is sensitive not only to the interatomic distance but also to the initial state of the system as well as to the properties of the optical element.