Universal dynamics on the way to thermalisation

It is demonstrated how a many-body system far from thermal equilibrium can exhibit universal dynamics in passing a non-thermal fixed point. As an example, the process of Bose-Einstein (BE) condensation of a dilute cold gas is considered. If the particle flux into the low-energy modes, induced, e.g., by a cooling quench, is sufficiently strong, the Bose gas develops a characteristic power-law single-particle spectrum $n(k)\sim k^{-5}$, and critical slowing down in time occurs. The fixed point is shown to be marked by the creation and dilution of tangled vortex lines. Alternatively, for a weak cooling quench and particle flux, the condensation process runs quasi adiabatically, passing by the fixed point in far distance, and signatures of critical scaling remain absent.Comment: 5+2 pages, 8 figure

Calculation of the microcanonical temperature for the classical Bose field

The ergodic hypothesis asserts that a classical mechanical system will in time visit every available configuration in phase space. Thus, for an ergodic system, an ensemble average of a thermodynamic quantity can equally well be calculated by a time average over a sufficiently long period of dynamical evolution. In this paper we describe in detail how to calculate the temperature and chemical potential from the dynamics of a microcanonical classical field, using the particular example of the classical modes of a Bose-condensed gas. The accurate determination of these thermodynamics quantities is essential in measuring the shift of the critical temperature of a Bose gas due to non-perturbative many-body effects.Comment: revtex4, 10 pages, 1 figure. v2: updated to published version. Fuller discussion of numerical results, correction of some minor error

Studies of Radiative Penguin B Decays at BaBar

We summarize results on a number of observations of penguin dominated radiative decays of the B meson. Such decays are forbidden at tree level and proceed via electroweak loops. As such they may be sensitive to physics beyond the standard model. The observations have been made at the BaBar experiment at PEP-II, the asymmetric B factory at SLAC.Comment: 3 pages, 5 figure

Motion of a condensate in a shaken and vibrating harmonic trap

The dynamics of a Bose-Einstein condensate (BEC) in a time-dependent harmonic trapping potential is determined for arbitrary variations of the position of the center of the trap and its frequencies. The dynamics of the BEC wavepacket is soliton-like. The motion of the center of the wavepacket, and the spatially and temporally dependent phase (which affects the coherence properties of the BEC) multiplying the soliton-like part of the wavepacket, are analytically determined.Comment: Accepted for publication in J. Phys. B: At Mol Opt Phy

Supercurrent Stability in a Quasi-1D Weakly Interacting Bose Gas

We discuss a possibility of observing superfluid phenomena in a quasi-1D weakly interacting Bose gas at finite temperatures. The weakness of interaction in combination with generic properties of 1D liquids can result in a situation when relaxational time of supercurrent is essentially larger than the time of experimental observation, and the behavior of the system is indistinguishable from that of a genuine superfluid.Comment: Revtex, 4 pages, no figures; Submitted to Phys. Rev. A (Brief Reports

Critical Dynamics of a Two-dimensional Superfluid near a Non-Thermal Fixed Point

Critical dynamics of an ultracold Bose gas far from equilibrium is studied in two spatial dimensions. Superfluid turbulence is created by quenching the equilibrium state close to zero temperature. Instead of immediately re-thermalizing, the system approaches a meta-stable transient state, characterized as a non-thermal fixed point. A focus is set on the vortex density and vortex-antivortex correlations which characterize the evolution towards the non-thermal fixed point and the departure to final (quasi-)condensation. Two distinct power-law regimes in the vortex-density decay are found and discussed in terms of a vortex binding-unbinding transition and a kinetic description of vortex scattering. A possible relation to decaying turbulence in classical fluids is pointed out. By comparing the results to equilibrium studies of a two-dimensional Bose gas, an intuitive understanding of the location of the non-thermal fixed point in a reduced phase space is developed.Comment: 11 pages, 13 figures; PRA versio

Quantum Glassiness

Describing matter at near absolute zero temperature requires understanding a system's quantum ground state and the low energy excitations around it, the quasiparticles, which are thermally populated by the system's contact to a heat bath. However, this paradigm breaks down if thermal equilibration is obstructed. This paper presents solvable examples of quantum many-body Hamiltonians of systems that are unable to reach their ground states as the environment temperature is lowered to absolute zero. These examples, three dimensional generalizations of quantum Hamiltonians proposed for topological quantum computing, 1) have no quenched disorder, 2) have solely local interactions, 3) have an exactly solvable spectrum, 4) have topologically ordered ground states, and 5) have slow dynamical relaxation rates akin to those of strong structural glasses.Comment: 4 page

Accidental suppression of Landau damping of the transverse breathing mode in elongated Bose-Einstein condensates

We study transverse radial oscillations of an elongated Bose-Einstein condensate using finite temperature simulations, in the context of a recent experiment at ENS. We demonstrate the existence of a mode corresponding to an in-phase collective oscillation of both the condensate and thermal cloud. Excitation of this mode accounts for the very small damping rate observed experimentally, and we find excellent quantitative agreement between experiment and theory. In contrast to other condensate modes, interatomic collisions are found to be the dominant damping mechanism in this case.Comment: 4 pages, 3 figure

Transformation of a Racemic Mixture by a Chiral Reagent or Catalyst to Give Regioisomeric Products

The transformation of a racemic mixture under the influence of a chiral reagent or catalyst is discussed in the case where regioisomeric products are obtained. The general relationships correlating the ee\u27s and the quantities of the various products are given. The special case of asymmetric Baeyer-Villiger oxidation of racemic ketones is taken as an example. Sometimes regioisomeric products are derived from opposite enantiomers, which implies that the re- gioselectivity of a reaction on an enantiomerically pure starting material will be controlled by the absolute configuration of the chiral reagent or catalyst