The Annular Shell Atom Trap (ASAT)

In the course of exploring some aspects of atom guiding in a hollow, optical fibre, a small negative potential energy well was found just in front of the repulsive or guiding barrier. This results from the optical dipole and the van der Waals potentials. The ground state for atoms bound in this negative potential well was determined by numerically solving the Schrödinger equation and it was found that this negative well could serve as an atom trap. This trap is referred to as the Annular Shell Atom Trap or ASAT because of the geometry of the trapped atoms which are located in the locus of points defining a very thin annular shell just in front of the guiding barrier. A unique feature of the ASAT is the compression of the atoms from the entire volume to the volume of the annular shell resulting in a very high density of atoms in this trap. This trap may have applications to very low temperatures using evaporative cooling and possibly the formation of BEC. Finally, a scheme is discussed for taking advantage of the de Broglie wavelength to store atoms in a bottle trap based on the inability of long de Broglie wavelengths to escape through a selective de Broglie wavelength filter in the atom bottle trap.     

Hydrogen trapping in helium damaged metals: a theoretical approach

A model which explains the trapping of hydrogen around or near helium bubbles is presented. According to this model, hydrogen atoms are attracted toward the bubbles due to positive stresses created by the very high pressure (350 kbar) existing inside the bubbles. The extreme trapping energy of hydrogen atoms around helium bubbles has been theoretically calculated and found to be 0.71 eV atom^–1. It is shown that most of the hydrogen atoms are trapped in a very small volume located very close to the bubble surface. The total hydrogen quantity was found to be in the range of 45–76 atoms per bubble for a wide range of hydrogen atom concentration, C. The good agreement between the theoretical results and data based on many experimental measurements reinforces the assumptions underlying the very basis of the suggested mechanism. The model proposed in this study can lead to better understanding of failure mechanisms.     

Heteronanojunctions with atomic size control using a lab-on-chip electrochemical approach with integrated microfluidics

A versatile tool for electrochemical fabrication of heteronanojunctions with nanocontacts made of a few atoms and nanogaps of molecular spacing is presented. By integrating microfluidic circuitry in a lab-on-chip approach, we keep control of the electrochemical environment in the vicinity of the nanojunction and add new versatility for exchanging and controlling the junction's medium. Nanocontacts made of various materials by successive local controlled depositions are demonstrated, with electrical properties revealing sizes reaching a few atoms only. Investigations on benchmark molecular electronics material, trapped between electrodes, reveal the possibility to create nanogaps of size matching those of molecules. We illustrate the interest of a microfluidic approach by showing that exposure of a fabricated molecular junction to controlled high solvent flows can be used as a reliability criterion for the presence of molecular entities in a gap.     

Optical Interface for Bose-Einstein Condensates Using Permanent Magnetic Traps and Cavity QED

We propose a new type of a hybrid architecture based on the interaction of magnetically trapped ultracold quantum gases in a cavity QED structure. Permanent magnetic traps are integrated with silica based cavity QEDs and waveguides to facilitate the interaction between the atomic Bose-Einstein condensates with optical fields on an atomchip. One of the advantages of the permanent magnetic traps is negligible technical noise, and thus minimal decoherence is achieved in comparison to other conventional methods using current-carrying-wires. The proposed design allows an efficient delivery of optical fields (control/probe) to the magnetically trapped atoms through the fabricated silica waveguides coupled to the micro-cavities. In addition to the control of the ultracold atoms, the optical interface allows for the possibility of connecting several nodes together on the same atom chip, and could be used as part of future quantum information processing devices.     

Detection of palladium by cold atom solution atomic absorption

One of the largest obstacles in miniaturizing traditional atomic spectroscopic sources is the need for a thermal/electrical source for free atom production. A single article in the literature has demonstrated atomic absorption detection of Ag, Cu, and Pd in solution at room temperature for atoms in the gas phase, which may ultimately permit miniaturization. Unfortunately, several laboratories have found that reproducing the phenomenon has been difficult. Without a sound fundamental explanation of the processes leading to the signal, one must conclude that it can be done, but some unsuspected and unknown design/methodological nuances are responsible for only a single reported success. Gas phase atoms could exist at room temperature "in solution" if the atoms were trapped in very small bubbles. In the current study, submicrometer-sized bubbles were created in a flow-through cell during the mixing of an alcohol-water solution containing a reducing agent with water containing the analyte. A repeatable atomic absorption signal was produced. Replacement of ethanol with 1-propanol and use of a surfactant increased the signal. Limits of detection of approximately 100 ppb in Pd were achieved, and it is estimated that approximately 0.4% of the Pd initially added is contained within the bubbles as gaseous atoms. The paper discusses the fundamental processes needed to achieve a repeatable signal.     

Optimization of geometry of heating neutral beam input into the TUMAN-3M tokamak

We consider the possibility of attaining a maximum contribution of energy to plasma due to variation in the impact parameter of a beam of high-energy neutral atoms and in the slope angle of the injection line to the equatorial plane at different parameters of the discharge. The influence of energy of particles on their confinement is also considered. It is shown that particles can be both passing and trapped depending on energy, which is connected with nonconservation of the adiabatic invariant W _⊥/B.     

Oxidation resistance of reactive atoms in graphene

We have found that reactive elements that are normally oxidized at room temperature are present as individual atoms or clusters on and in graphene. Oxygen is present in these samples but it is only detected in the thicker amorphous carbon layers present in the graphene specimens we have examined. However, we have seen no evidence that oxygen reacts with the impurity atoms and small clusters of these normally reactive elements when they are incorporated in the graphene layers. First principles calculations suggest that the oxidation resistance is due to kinetic effects such as preferential bonding of oxygen to nonincorporated atoms and H passivation. The observed oxidation resistance of reactive atoms in graphene may allow the use of these incorporated metals in catalytic applications. It also opens the possibility of designing and producing electronic, opto-electronic, and magnetic devices based on these normally reactive atoms.     

Thermally Induced Losses in Ultra-Cold Atoms Magnetically Trapped Near Room-Temperature Surfaces

We have measured magnetic trap lifetimes of ultra-cold ⁸⁷Rb atoms at distances of 5–1000 µm from surfaces of conducting metals with varying resistivity. Good agreement is found with a theoretical model for losses arising from near-field magnetic thermal noise, confirming the complications associated with holding trapped atoms close to conducting surfaces. A dielectric surface (silicon) was found in contrast to be so benign that we are able to evaporatively cool atoms to a Bose–Einstein condensate by using the surface to selectively adsorb higher energy atoms.     

Entanglement generation in atom-cavity networks with complete connectivity

In this paper, we consider the situation that four identical two-level atoms are separately trapped in separated tetrahedral structure single-mode optical cavities, which are placed at the vertices of a tetrahedron and are coupled by four fibres. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the Schrödinger equation when the total excitation number of the system equals one. Negativity is adopted to quantify the degree of entanglement between two subsystems. The entanglement dynamics between atoms and between cavities is studied. The influences of atom-cavity coupling coefficient on the entanglement between atoms and that between cavities are discussed. The results obtained using the numerical method show that the atom–atom entanglement and the cavity–cavity entanglement are all strengthened with increase of atom-cavity coupling coefficient.     

CHROMATOGRAPHIC PURIFICATION OF Kr@C60

Unusual compounds have been reported to form by the incorporation of atoms into fullerene cages. The compounds in which a noble gas atom is trapped into a C₆₀ cage are very stable and only van der Waals interactions occur between the noble gas and the fullerene cage. The study of these compounds requires efficient chromatographic (or other) separations. We performed the isolation of Kr@C₆₀ and a study of its chromatographic separations on several HPLC columns using toluene : hexane mixtures as solvent. We found that the separation factor is small (1.09 to 1.12) with the highest separation factor on a Buckyprep column.     

CHROMATOGRAPHIC PURIFICATION OF Kr@C60

Unusual compounds have been reported to form by the incorporation of atoms into fullerene cages. The compounds in which a noble gas atom is trapped into a C₆₀ cage are very stable and only van der Waals interactions occur between the noble gas and the fullerene cage. The study of these compounds requires efficient chromatographic (or other) separations. We performed the isolation of Kr@C₆₀ and a study of its chromatographic separations on several HPLC columns using toluene : hexane mixtures as solvent. We found that the separation factor is small (1.09 to 1.12) with the highest separation factor on a Buckyprep column.     

Stability of Two-Component Bose-Einstein Condensates in Traps

Static and dynamic stabilities of two-component Bose-Einstein condensates trapped in harmonic potentials are studied. Using the variational method, we obtain the static stability condition and the phase separation condition. They are expressed as functions of the particle numbers and the s-wave scattering lengths. We find that the interaction between the different species of atoms (simply, interspecies interaction) has significant effects on the stability of each condensate. The instability of the ground state is explained in terms of the lowering (softening) of the collective excitation energies. We investigate the low-lying excitations and the possibility of their softening by use of the Gaussian ansatz and the sum-rule approach.     

Quantum dynamics of the phase of a Bose–Einstein condensate

Abstract

In this review we discuss the dynamics of the phase of trapped Bose–Einstein condensates. In particular we consider the phenomena of phase decoherence (termed also as phase collapse, or diffusion), and phase revival in systems of interacting atoms. We analyse the dependence of the collapse and revival times on the trap potential, dimensionality of the gas, atom number fluctuations, and on the coherent dynamics of the condensate. We show that in a class of experimentally relevant systems, the collapse time is relatively short, and in some cases vanishes in the limit of a large number of atoms, implying that the trapped Bose gas cannot sustain a well-defined quantum phase, and that the phase memory is lost on a relatively short time scale. Furthermore, we calculate the relative atom number fluctuations or a model of two interacting condensates, and show that the fluctuations are generically sub-Poissonian.     

Frozen geometric discord in dissipative cavity quantum electrodynamics system

We investigate the dynamics of geometric quantum correlations for certain decoherence channels and discuss the necessary conditions for the existence of frozen geometric discord. As illustrative examples, we study the phenomenon of double sudden transitions in geometric discord for a system consisting of two noninteracting atoms inserted in two independent dissipative cavities and how the initial state parameters and decay rate of dissipative cavities affect the frozen time during which the geometric discord remains constant. We also explore the dynamics of geometric discord between two noninteracting atoms trapped in a common dissipative cavity and find that the geometric discord exhibits sudden transition between classical and quantum decoherence. Moreover, a nonzero stationary geometric discord can arise in both the independent cavity case and common cavity case.     

The solubility of spin-polarized3He in4He and the superfluidity of3He in3He-4He mixtures

We investigate the possibility of a large enhancement of the T = 0 finite solubility of³He in⁴He due to spin-polarization. The size of the effect depends on the fraction of³He atoms in the system. We present two different approaches for the limits of a small and a large number of³He atoms compared to the number of⁴He atoms. Since the possible³He superfluid phase transition depends on³He density, we calculate the consequences of this change in the solubility for its superfluid transition temperature. It is shown that for small fractions of³He, the transition temperature is enhanced mostly due to the enlargement of the up-spin Fermi sphere. In the opposite limit the transition temperature is enhanced as a result of the increased³He solubility.     

Trapping Fermionic 40K and Bosonic 87Rb on a Chip

We demonstrate the loading of a Bose–Fermi mixture into a microfabricated magnetic trap. In a single-chamber vacuum system, laser-cooled atoms are transported to the surface of a substrate on which gold wires have been microfabricated. The magnetic field minimum formed near these current-carrying wires is used to confine up to 6 × 10⁴ neutral ⁴⁰K atoms. In addition, we can simultaneously load 2 × 10^{5 87}Rb atoms, demonstrating the confinement of two distinct elements with such a trap. In a sequence optimized for ⁸⁷Rb alone, we observe up to 1 × 10⁷ trapped atoms. We describe in detail the experimental apparatus, and discuss prospects for evaporative cooling towards quantum degeneracy in both species.     

Zero-temperature Properties of Attractive Bose-Einstein Condensate by Correlated Many-body Approach

We employ a correlated many-body approach to study Bose-Einstein condensation of a magnetically trapped gas of ⁷Li atoms. The properties of a trapped gas are strongly influenced by the attractive interactions and two-body correlations. The correlations lower the interaction energy. The lowlying collective frequencies have also been calculated. In addition we explore the frequency of surface modes as a function of angular momentum.     

Two-Fluid Hydrodynamics in Trapped Bose Gases and in Superfluid Helium

A review is given of recent theoretical work on the superfluid dynamics of trapped Bose gases at finite temperatures, where there is a significant fraction of non-condensate atoms. One can now reach large enough densities and collision cross-sections needed to probe the collective modes in the collision-dominated hydrodynamic region where the gas exhibits characteristic superfluid behavior involving the relative motions of the condensate and non-condensate components. The precise analogue of the Landau-Khalatnikov two-fluid hydrodynamic equations was recently derived from trapped Bose gases, starting from a generalized Gross-Pitaevskii equation for the condensate macroscopic wavefunction and a kinetic equation for the non-condensate atoms.     

Preliminary results of the trapped atom clock on a chip

We present an atomic clock based on the interrogation of magnetically trapped ⁸⁷Rb atoms. Two photons, in the microwave and radiofrequency domain, excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F = 1, m_F = -1? to |F = 2, m_F = 1? is 1st-order insensitive to magnetic field variations. Ramsey interrogation times longer than 2 s can be achieved, leading to a projected clock stability in the low 10^-13 at 1 s for a cloud of 10⁵ atoms. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5 cm)³. We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25 Hz.     

Radiochemical approaches for formation of endohedral fullerenes and MD simulation

The formation of atom-doped fullerenes has been investigated by using several types of radionuclides produced by nuclear reactions. From the trace of the radioactivities after a high performance liquid chromatography, it was found that formation of endohedral fullerenes (or heterofullerenes) of small atoms (Be, Li), noble-gas atoms (Kr, Xe) and 4B–6B elements (Ge, As, Se, Sb, Te, etc.) is possible by a recoil process following the nuclear reaction. In order to show the possibility of creating endohedral fullerenes with a suitably high kinetic energy of foreign atoms, we have carried out large-scale ab initio molecular dynamics simulations on the basis of the all-electron mixed-basis approach with atomic orbitals and plane waves for several atoms.