Total Current Blockade in an Ultracold Dipolar Quantum Wire

in Physical Review Letters (2013), 110

Cold-atom systems offer a great potential for the future design of new mesoscopic quantum systems with properties that are fundamentally different from semiconductor nanostructures. Here, we investigate ... [more ▼]

Cold-atom systems offer a great potential for the future design of new mesoscopic quantum systems with properties that are fundamentally different from semiconductor nanostructures. Here, we investigate the quantum-gas analogue of a quantum wire and find a new scenario for the quantum transport: Attractive interactions may lead to a complete suppression of current in the low-bias range, a total current blockade. We demonstrate this effect for the example of ultracold quantum gases with dipolar interactions. [less ▲]

1D many-body quantum transport of Bose-Einstein condensates : a truncated Wigner approach

Poster (2012, March 29)

We calculate the transport properties of an ultracold gas of Bose- Einstein condensed atoms that is coupled from a magnetic trap into a one-dimensional waveguide. A central aim of such guided atom lasers ... [more ▼]

We calculate the transport properties of an ultracold gas of Bose- Einstein condensed atoms that is coupled from a magnetic trap into a one-dimensional waveguide. A central aim of such guided atom lasers is to study the role of atom-atom interaction in many-body transport processes across finite scattering regions within the waveguide resembling tunnel junctions and quantum dots. Our numerical approach to solve this many-body scattering problem is based on a home-made theory where the boundaries of the system are simulating an open system enabling us to calulate observable in the steady-state regime such as density, current, transmission. The results are compared to the mean-field regime. [less ▲]

Weak localization with nonlinear bosonic matter waves

in Annals of Physics (2012), 327

We investigate the coherent propagation of dilute atomic Bose-Einstein condensates through irregularly shaped billiard geometries that are attached to uniform incoming and outgoing waveguides. Using the ... [more ▼]

We investigate the coherent propagation of dilute atomic Bose-Einstein condensates through irregularly shaped billiard geometries that are attached to uniform incoming and outgoing waveguides. Using the mean-field description based on the nonlinear Gross–Pitaevskii equation, we develop a diagrammatic theory for the self-consistent stationary scattering state of the interacting condensate, which is combined with the semiclassical representation of the single-particle Green function in terms of chaotic classical trajectories within the billiard. This analytical approach predicts a universal dephasing of weak localization in the presence of a small interaction strength between the atoms, which is found to be in good agreement with the numerically computed reflection and transmission probabilities of the propagating condensate. The numerical simulation of this quasi-stationary scattering process indicates that this interaction-induced dephasing mechanism may give rise to a signature of weak antilocalization, which we attribute to the influence of non-universal short-path contributions. [less ▲]

Effective spin model for interband transport in a Wannier-Stark lattice system

in European Physical Journal D -- Atoms, Molecules, Clusters & Optical Physics (2011), 63

We show that the interband dynamics in a tilted two-band Bose-Hubbard model can be reduced to an analytically accessible spin model in the case of resonant interband oscillations. This allows us to ... [more ▼]

We show that the interband dynamics in a tilted two-band Bose-Hubbard model can be reduced to an analytically accessible spin model in the case of resonant interband oscillations. This allows us to predict the revival time of these oscillations which decay and revive due to inter-particle interactions. The presented mapping onto the spin model and the so achieved reduction of complexity has interesting perspectives for future studies of many-body systems. [less ▲]

Transport of ultracold Bose gases beyond the Gross-Pitaevskii description

in Physical Review. A : General Physics (2010), 81(1), 013631

We explore atom-laser-like transport processes of ultracold Bose-condensed atomic vapors in mesoscopic waveguide structures beyond the Gross-Pitaevskii mean-field theory. Based on a microscopic ... [more ▼]

We explore atom-laser-like transport processes of ultracold Bose-condensed atomic vapors in mesoscopic waveguide structures beyond the Gross-Pitaevskii mean-field theory. Based on a microscopic description of the transport process in the presence of a coherent source that models the outcoupling from a reservoir of perfectly Bose-Einstein condensed atoms, we derive a system of coupled quantum evolution equations that describe the dynamics of a dilute condensed Bose gas in the framework of the Hartree-Fock-Bogoliubov approximation. We apply this method to study the transport of dilute Bose gases through an atomic quantum dot and through waveguides with disorder. Our numerical simulations reveal that the onset of an explicitly time-dependent flow corresponds to the appearance of strong depletion of the condensate on the microscopic level and leads to a loss of global phase coherence. [less ▲]

Transport and interaction blockade of cold bosonic atoms in a triple-well potential

in New Journal of Physics (2010), 12

We theoretically investigate the transport properties of cold bosonic atoms in a quasi-one-dimensional (1D) triple-well potential that consists of two large outer wells, which act as microscopic source ... [more ▼]

We theoretically investigate the transport properties of cold bosonic atoms in a quasi-one-dimensional (1D) triple-well potential that consists of two large outer wells, which act as microscopic source and drain reservoirs, and a small inner well, which represents a quantum-dot-like scattering region. Bias and gate 'voltages' introduce a time-dependent tilt of the triple-well configuration, and are used to shift the energetic level of the inner well with respect to the outer ones. By means of exact diagonalization considering a total number of six atoms in the triple-well potential, we find diamond-like structures for the occurrence of single-atom transport in the parameter space spanned by the bias and gate voltages. We discuss the analogy with Coulomb blockade in electronic quantum dots, and point out how one can infer the interaction energy in the central well from the distance between the diamonds. [less ▲]

Coherent backscattering of Bose-Einstein condensates in two-dimensional disorder potentials

in Physical Review Letters (2008), 101(2), 020603

We study quantum transport of an interacting Bose-Einstein condensate in a two-dimensional disorder potential. In the limit of a vanishing atom-atom interaction, a sharp cone in the angle-resolved density ... [more ▼]

We study quantum transport of an interacting Bose-Einstein condensate in a two-dimensional disorder potential. In the limit of a vanishing atom-atom interaction, a sharp cone in the angle-resolved density of the scattered matter wave is observed, arising from constructive interference between amplitudes propagating along reversed scattering paths. Weak interaction transforms this coherent backscattering peak into a pronounced dip, indicating destructive instead of constructive interference. We reproduce this result, obtained from the numerical integration of the Gross-Pitaevskii equation, by a diagrammatic theory of weak localization in the presence of nonlinearity. [less ▲]

Nonexponential decay of Bose-Einstein condensates: a numerical study based on the complex scaling method

in Applied Physics B : Lasers & Optics (2007), 86(3), 385-390

We study the decay dynamics of an interacting Bose-Einstein condensate in the presence of a metastable trapping potential from which the condensate can escape via tunneling through finite barriers. The ... [more ▼]

We study the decay dynamics of an interacting Bose-Einstein condensate in the presence of a metastable trapping potential from which the condensate can escape via tunneling through finite barriers. The time-dependent decay process is reproduced by means of the instantaneous decay rates of the condensate at a given population of the quasi-bound state, which are calculated with the method of complex scaling. Both for the case of a double-barrier potential as well as for the case of a tilted periodic potential, we find pronounced deviations from a monoexponential decay behavior, which would generally be expected in the absence of the atom-atom interaction. [less ▲]

Nonlinear transport of Bose-Einstein condensates through mesoscopic waveguides

in Physical Review. A (2007), 76(6),

We study the coherent flow of interacting Bose-condensed atoms in mesoscopic waveguide geometries. Analytical and numerical methods, based on the mean-field description of the condensate, are developed to ... [more ▼]

We study the coherent flow of interacting Bose-condensed atoms in mesoscopic waveguide geometries. Analytical and numerical methods, based on the mean-field description of the condensate, are developed to study both stationary as well as time-dependent propagation processes. We apply these methods to the propagation of a condensate through an atomic quantum dot in a waveguide, discuss the nonlinear transmission spectrum and show that resonant transport is generally suppressed due to an interaction-induced bistability phenomenon. Finally, we establish a link between the nonlinear features of the transmission spectrum and the self-consistent quasibound states of the quantum dot. [less ▲]

Tunneling in Presence of Chaos and Interactions

Post doctoral thesis (2006)