Vortex lattices in the lowest Landau level for confined Bose-Einstein condensates

We present the results of numerical calculations of the groundstates of weakly-interacting Bose-Einstein condensates containing large numbers of vortices. Our calculations show that these groundstates appear to be close to uniform triangular vortex lattices. However, slight deviations from a uniform triangular lattice have dramatic consequences on the overall particle distribution. In particular, we demonstrate that the overall particle distribution averaged on a lengthscale large compared to the vortex lattice constant is well approximated by a Thomas-Fermi profile.Comment: 5 pages, 4 figure

Impact-induced acceleration by obstacles

We explore a surprising phenomenon in which an obstruction accelerates, rather than decelerates, a moving flexible object. It has been claimed that the right kind of discrete chain falling onto a table falls \emph{faster} than a free-falling body. We confirm and quantify this effect, reveal its complicated dependence on angle of incidence, and identify multiple operative mechanisms. Prior theories for direct impact onto flat surfaces, which involve a single constitutive parameter, match our data well if we account for a characteristic delay length that must impinge before the onset of excess acceleration. Our measurements provide a robust determination of this parameter. This supports the possibility of modeling such discrete structures as continuous bodies with a complicated constitutive law of impact that includes angle of incidence as an input.Comment: small changes and corrections, added reference

Approximate solution of a flow over a ramp for large Froude number

AbstractAn approximate method is presented to solve the problem of steady free-surface flow of an ideal fluid over a semi-infinite ramp in the bottom. Schwartz-Christoffel transformation is used to map the region of flow, in the complex potential-plane, onto the upper half-plane. The Hilbert transformation as well as the perturbation technique are used as a basis for the approximate solution of the problem for large Froude number and small inclination angle of the ramp. General equations, in integral form, for any order of approximation are obtained. Solution up to first-order approximation is discussed and illustrated.Elevation of the free-surface for different ramp heights, different inclination angles of the ramp and different Froude numbers are plotted. An approximate formula of maximum elevation of the free-surface in terms of the ramp heights and its inclination angle is found

Onset of Interlayer Phase Coherence in a Bilayer Two-Dimensional Electron System: Effect of Layer Density Imbalance

Tunneling and Coulomb drag are sensitive probes of spontaneous interlayer phase coherence in bilayer two-dimensional electron systems at total Landau level filling factor $\nu_T = 1$. We find that the phase boundary between the interlayer phase coherent state and the weakly-coupled compressible phase moves to larger layer separations as the electron density distribution in the bilayer is imbalanced. The critical layer separation increases quadratically with layer density difference.Comment: 4 pages, 3 figure

Pattern of Reaction Diffusion Front in Laminar Flows

Autocatalytic reaction between reacted and unreacted species may propagate as solitary waves, namely at a constant front velocity and with a stationary concentration profile, resulting from a balance between molecular diffusion and chemical reaction. The effect of advective flow on the autocatalytic reaction between iodate and arsenous acid in cylindrical tubes and Hele-Shaw cells is analyzed experimentally and numerically using lattice BGK simulations. We do observe the existence of solitary waves with concentration profiles exhibiting a cusp and we delineate the eikonal and mixing regimes recently predicted.Comment: 4 pages, 3 figures. This paper report on experiments and simulations in different geometries which test the theory of Boyd Edwards on flow advection of chemical reaction front which just appears in PRL (PRL Vol 89,104501, sept2002

Formation of atomic tritium clusters and condensates

We present an extensive study of the static and dynamic properties of systems of spin-polarized tritium atoms. In particular, we calculate the two-body |F,m_F>=|0,0> s-wave scattering length and show that it can be manipulated via a Feshbach resonance at a field strength of about 870G. Such a resonance might be exploited to make and control a Bose-Einstein condensate of tritium in the |0,0> state. It is further shown that the quartet tritium trimer is the only bound hydrogen isotope and that its single vibrational bound state is a Borromean state. The ground state properties of larger spin-polarized tritium clusters are also presented and compared with those of helium clusters.Comment: 5 pages, 3 figure

Measuring the condensate fraction of rapidly rotating trapped boson systems: off-diagonal order from the density

We demonstrate a direct connection between the density profile of a system of ultra-cold trapped bosonic particles in the rapid-rotation limit and its condensate fraction. This connection can be used to probe the crossover from condensed vortex-lattice states to uncondensed quantum fluid states that occurs in rapidly rotating boson systems as the particle density decreases or the rotation frequency increases. We illustrate our proposal with a series of examples, including ones based on models of realistic finite trap systems, and comment on its application to freely expanding boson density profile measurements.Comment: 4 pages, 3 figures, version accepted for publication in Phys. Rev. Let

Spin Transition in Strongly Correlated Bilayer Two Dimensional Electron Systems

Using a combination of heat pulse and nuclear magnetic resonance techniques we demonstrate that the phase boundary separating the interlayer phase coherent quantum Hall effect at $\nu_T = 1$ in bilayer electron gases from the weakly coupled compressible phase depends upon the spin polarization of the nuclei in the host semiconductor crystal. Our results strongly suggest that, contrary to the usual assumption, the transition is attended by a change in the electronic spin polarization.Comment: 4 pages, 3 postscript figur

Charge Imbalance and Bilayer 2D Electron Systems at νT=1\nu_T = 1

We use interlayer tunneling to study bilayer 2D electron systems at $\nu_T = 1$ over a wide range of charge density imbalance, $\Delta \nu =\nu_1-\nu_2$, between the two layers. We find that the strongly enhanced tunneling associated with the coherent excitonic $\nu_T = 1$ phase at small layer separation can survive at least up to an imbalance of $\Delta \nu$ = 0.5, i.e $(\nu_1, \nu_2)$ = (3/4, 1/4). Phase transitions between the excitonic $\nu_T = 1$ state and bilayer states which lack significant interlayer correlations can be induced in three different ways: by increasing the effective interlayer spacing $d/\ell$, the temperature $T$, or the charge imbalance, $\Delta \nu$. We observe that close to the phase boundary the coherent $\nu_T = 1$ phase can be absent at $\Delta \nu$ = 0, present at intermediate $\Delta \nu$, but then absent again at large $\Delta \nu$, thus indicating an intricate phase competition between it and incoherent quasi-independent layer states. At zero imbalance, the critical $d/\ell$ shifts linearly with temperature, while at $\Delta \nu$ = 1/3 the critical $d/\ell$ is only weakly dependent on $T$. At $\Delta \nu$ = 1/3 we report the first observation of a direct phase transition between the coherent excitonic $\nu_T = 1$ bilayer integer quantum Hall phase and the pair of single layer fractional quantized Hall states at $\nu_1$ = 2/3 and $\nu_2=1/3$.Comment: 13 pages, 8 postscript figures. Final published versio