The irreversible transport of multi-component Bose-Einstein condensate (BEC) is investigated within the Stimulated Adiabatic Raman Passage (STIRAP) scheme. A general formalism for a single BEC in M-well trap is derived and analogy between multi-photon and tunneling processes is demonstrated. STIRAP transport of BEC in a cyclic triple-well trap is explored for various values of detuning and interaction between BEC atoms. It is shown that STIRAP provides a complete population transfer at zero detuning and interaction and persists at their modest values. The detuning is found not to be obligatory. The possibility of non-adiabatic transport with intuitive order of couplings is demonstrated. Evolution of the condensate phases and generation of dynamical and geometric phases are inspected. It is shown that STIRAP allows to generate the unconventional geometrical phase which is now of a keen interest in quantum computing.Comment: 9 pages, 6 figures. To be published in Laser Physics (v. 19, n.4, 2009

By using a close similarity between multi-photon and tunneling population transfer schemes, we propose robust adiabatic methods for the transport of Bose-Einstein condensate (BEC) in doubleand triple-well traps. The calculations within the mean-field approximation (Gross-Pitaevskii equation) show that irreversible and complete transport takes place even in the presence of the nonlinear effects caused by interaction between BEC atoms. The transfer is driven by adiabatic timedependent monitoring the barriers and well depths. The proposed methods are universal and can be applied to a variety of systems and scenarios.

We show that there exists the inverse Kibble-Zurek scenario, when we start with an equilibrium system with broken symmetry and, by imposing perturbations, transform it to a strongly nonequilibrium symmetric state through the sequence of states with spontaneously arising topological defects. We demonstrate the inverse Kibble-Zurek scenario both experimentally, by perturbing the Bose-Einstein condensate of trapped 87 Rb atoms, and also by accomplishing numerical simulations for the same setup as in the experiment, the experimental and numerical results being in good agreement with each other.

In this paper we considered a quantum particle moving through delute Bose-Einstein condensate at zero temperature. In our formulation the impurity particle interacts with the gas of uncoupled Bogoliubov's excitations. We constructed the perturbation theory for the Green's function of the impurity particle with respect to the impurity-condensate interaction employing the coherent-state path integral approach. The perturbative expansion for the Green's function is resumed into the expansion for its poles with the help of the diagrammatic technique developed in this work. The dispersion relation for the impurity clothed by condensate excitations is obtained and effective mass is evaluated beyond the Golden rule approximation.Typeset by REVT E X

International audienceStructure and properties of SrO-Al$_2$O$_3$-SiO$_2$ glasses and melts were investigated along the tectosilicate join (SrO/Al$_2$O$_3$ = 1), varying the amount of silica. The structure of the glasses was studied by means of various spectroscopic techniques: Raman, $^{27}$Al NMR and XAS at the Sr K-edge. Raman spectroscopy revealed that the fraction of high-membered tetrahedral rings diminishes upon substitution of SiO$_2$ by SrAl$_2$O$_4$ favouring the formation of low-membered rings.Sr K-edge XANES shows that the strontium coordination number is around 9, based on the spectrum similarity with the one obtained for crystalline strontianite. $^{27}$Al NMR spectroscopy indicates the presence of four- and five-coordinated aluminium the latter being found in small quantities (< 5%), i.e. smaller than for analogous Mg- and Ca-based aluminosilicate glasses. A minimum in $T_g$ is found when the AlO$_5$ content is maximum, both in Sr and Ca aluminosilicates. This fact indicates the importance of minor species such as five-fold aluminium in activating viscous flow, similarly to what has been proposed for five-fold silicon by Farnan and Stebbins (1994). Increase of $T_g$ at low silica content was correlated to a decrease in AlO$_5$ content as well as to a decrease of a number of different structural units and, as a consequence, an ordering of the system

We present experimental observations and numerical simulations of nonequilibrium spatial structures in a trapped Bose-Einstein condensate subject to oscillatory perturbations. In experiment, first, there appear collective excitations, followed by quantum vortices. Increasing the amount of the injected energy leads to the formation of vortex tangles representing quantum turbulence. We study what happens after the regime of quantum turbulence, with increasing further the amount of injected energy. In such a strongly nonequilibrium Bosecondensed system of trapped atoms, vortices become destroyed and there develops a new kind of spatial structure exhibiting essentially heterogeneous spatial density. The structure is reminiscent of fog consisting of high-density droplets, or grains, surrounded by the regions of low density. The grains are randomly distributed in space, where they move. They live for a sufficiently long time to be treated as a type of metastable object. Such structures have been observed in nonequilibrium trapped Bose gases of 87 Rb, subject to the action of alternating fields. Here we present experimental results and support them by numerical simulation. The granular, or fog structure is essentially different from the state of wave turbulence that develops after increasing further the amount of injected energy.

This is the final published version of the article (version of record). It first appeared online via APS at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.064203. Please refer to any applicable terms of use of the publisher. University of Bristol -Explore Bristol Research General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. The atomic-scale structure of aerodynamically levitated and laser-heated liquid tricalcium aluminate (Ca 3 Al 2 O 6 ) was measured at 2073(30) K by using the method of neutron diffraction with Ca isotope substitution (NDIS). The results enable the detailed resolution of the local coordination environment around calcium and aluminum atoms, including the direct determination of the liquid partial structure factor, S CaCa (Q), and partial pair distribution function, g CaCa (r). Molecular dynamics (MD) simulation and reverse Monte Carlo (RMC) refinement methods were employed to obtain a detailed atomistic model of the liquid structure. The composition Ca 3 Al 2 O 6 lies at the CaO-rich limit of the CaO:Al 2 O 3 glass-forming system. Our results show that, although significantly depolymerized, liquid Ca 3 Al 2 O 6 is largely composed of AlO 4 tetrahedra forming an infinite network with a slightly higher fraction of bridging oxygen atoms than expected for the composition. Calcium-centered polyhedra exhibit a wide distribution of four-to sevenfold coordinated sites, with higher coordinated calcium preferentially bonding to bridging oxygens. Analysis of the MD configuration reveals the presence of ∼10 % unconnected AlO 4 monomers and Al 2 O 7 dimers in the liquid. As the CaO concentration increases, the number of these isolated units increases, such that the upper value for the glass-forming composition of CaO:Al 2 O 3 liquids could be described in terms of a percolation threshold at which the glass can no longer support the formation of an infinitely connected AlO 4 network.

The structure of strontium glasses with the composition (SiO)(AlO) (SrO) ( R = [SrO]/[AlO] = 1) and (SiO)(AlO) (SrO) ( R = 3) has been explored experimentally over both short- and intermediate-length scales using neutron diffraction, Al andSi nuclear magnetic resonance, and classical molecular dynamics simulations in model systems containing around 10 000 atoms. We aim at understanding the structural role of aluminum and strontium as a function of the chemical composition of these glasses. The short- and medium-range structure such as aluminum coordination, bond angle distribution, Q distribution, and oxygen speciation have been systematically studied. Two potential forms of the repulsive short-range interactions have been investigated, namely, the Buckingham and Morse forms. The comparison of these forms allows us to derive general trends independent of the particular choice of the potential form. In both cases, it is found that aluminum ions are mainly fourfold coordinated and mix with the silicon network favoring the Al/Si mixing in terms of Al-O-Si linkages. For the R = 1 glass series, despite the full charge compensation ([SrO] = [AlO]), a small fraction of fivefold aluminum is observed both experimentally and in MD simulations, whereas the concentration of sixfold aluminum is negligible. MD shows that the fivefold aluminum units AlO preferentially adopt a small ring configuration and link to tricoordinated oxygen atoms whose population increases with the aluminum content and are mainly found in OAl and OAlSi configurations. The modeled Sr speciation mainly involves SrO and SrO polyhedra, giving a range of average Sr coordination numbers between 7 and 8 slightly dependent on the short-range repulsive potential form. A detailed statistical analysis of T-O-T' (T, T' = Al,Si), accounting for the population of the various oxygen speciations, reveals that both potentials predict a nearly identical Al/Si mixing.