Macroscopic Quantum Self-Trapping in Dynamical Tunnelling

It is well-known that increasing the nonlinearity due to repulsive atomic interactions in a double-well Bose-Einstein condensate suppresses quantum tunnelling between the two sites. Here we find analogous behaviour in the dynamical tunnelling of a Bose-Einstein condensate between period-one resonances in a single driven potential well. For small nonlinearities we find unhindered tunnelling between the resonances, but with an increasing period as compared to the non-interacting system. For nonlinearities above a critical value we generally observe that the tunnelling shuts down. However, for certain regimes of modulation parameters we find that dynamical tunnelling re-emerges for large enough nonlinearities, an effect not present in spatial double-well tunnelling. We develop a two-mode model in good agreement with full numerical simulations over a wide range of parameters, which allows the suppression of tunnelling to be attributed to macroscopic quantum self-trapping.Comment: 5 pages, 3 figure

The forward photon production and the gluonic content of the real and virtual photon at the HERA collider

The discussion on the production of prompt photons with pT of a few GeV in the tagged process ep -> e gamma X with small Q^2 (DIC process) at the HERA collider is presented. Photons produced in the forward (proton) direction are mainly originating from subprocesses involving interactions of the gluonic content of the exchanged photon. The large enhancement over the Born term (direct photon) is found up to a factor of 35 for a real photon and up to 5 for a virtual photon with a squared virtuality 1 GeV^2. It gives a possibility of extracting a gluonic density of the real and of the virtual photon. The BFKL approach to the description of the forward particle production is shortly discussed.Comment: 7 pages, 2 ps figures, latex using psfig.sty and axodraw.sty. Presented at the International Conference on the Structure and Interactions of the Photon, PHOTON'99, 23-27 May 1999, Freiburg im Breisgan, German

Formation of matter-wave soliton molecules

We propose a method of forming matter-wave soliton molecules that is inspired by the recent experiment of Dris {\it et al.}. In the proposed set-up we show that if two solitons are initially prepared in phase and with a sufficiently small separation and relative velocity, a bound pair will always form. This is verified by direct numerical simulation of the Gross-Pitaevskii equation and by the derivation of the exact interaction energy of two solitons, which takes the form of a Morse potential. This interaction potential depends not only on the separation but also on the relative phase of the solitons and is essential for an analytical treatment of a host of other problems, such as the soliton gas and the Toda lattice of solitons.Comment: 4 pages, 3 figure

Squeezed coherent state undergoing a continuous nondemolition observation

The time evolution of a squeezed coherent state conditioned by the results of a single and double heterodyne measurement is discussed. The mean values of quadratures as well as the dynamics of quadrature uncertainties have been obtained within the framework of the theory of continuous measurements based on filtration equations. It has been found that while the mean values depend on the measured noise, the uncertainties in the optical quadratures are deterministic. Explicit solutions for the latter have been provided. Finally, a time development of the squeeze parameter for the posterior squeezed coherent state has been found.Comment: Some minor corrections have been mad

Dynamical formation of bright solitons in the collapse of bose-einstein condensates

We model the formation of bright atomic solitons due to collapse of Bose-Einstein condensates with attractive interactions reported by S. L. Cornish et al., [Phys. Rev. Lett. 96 170401 (2006)] in a realistic three dimensional situation. We show that mean-field theory does not adequately explain the experiment, while the inclusion of quantum fluctuations gives rise to bright soliton formation at the appropriate time scales. The solitons are produced either in-phase or out-of-phase and their number increases with the strength of the attractive interaction

The Size and Shape of Caldesmon and Its Fragments in Solution Studied by Dynamic Light Scattering and Hydrodynamic Model Calculations

The size and the shape of caldesmon as well as its 50-kDa central and 19-kDa C-terminal fragments were investigated by photon correlation spectroscopy. The hydrodynamic radii, which have been calculated from the experimentally obtained translational diffusion coefficients, are 9.8 nm, 6.0 nm, and 2.9 nm, respectively. Moreover, the experimental values for the translational diffusion coefficients are compared with results obtained from hydrodynamic model calculations. Detailed models for the structure of caldesmon in solution are derived. The contour length is about 64 nm for all of the models used for caldesmon