675 research outputs found
Inter-species Tunneling in One-dimensional Bose Mixtures
We study the ground-state properties and quantum dynamics of few-boson
mixtures with strong inter-species repulsion in one-dimensional traps. If one
species localizes at the center, e.g., due to a very large mass compared to the
other component, it represents an effective barrier for the latter and the
system can be mapped onto identical bosons in a double well. For weaker
localization, the barrier atoms begin to respond to the light component,
leading to an induced attraction between the mobile atoms that may even
outweigh their bare intra-species repulsion. To explain the resulting effects,
we derive an effective Hubbard model for the lighter species accounting for the
backaction of the barrier in correction terms to the lattice parameters. Also
the tunneling is drastically affected: Varying the degree of localization of
the "barrier" atoms, the dynamics of intrinsically noninteracting bosons can
change from Rabi oscillations to effective pair tunneling. For identical
fermions (or fermionized bosons) this leads to the tunneling of attractively
bound pairs.Comment: 13 pages, 11 figures; v2 reflects major revisio
VR/Urban: spread.gun - design process and challenges in developing a shared encounter for media façades
Designing novel interaction concepts for urban environments is not only a technical challenge in terms of scale, safety, portability and deployment, but also a challenge of designing for social configurations and spatial settings. To outline what it takes to create a consistent and interactive experience in urban space, we describe the concept and multidisciplinary design process of VR/Urban's media intervention tool called Spread.gun, which was created for the Media Façade Festival 2008 in Berlin. Main design aims were the anticipation of urban space, situational system configuration and embodied interaction. This case study also reflects on the specific technical, organizational and infrastructural challenges encountered when developing media façade installations
Material-barrier Tunneling in One-dimensional Few-boson Mixtures
We study the quantum dynamics of strongly interacting few-boson mixtures in
one-dimensional traps. If one species is strongly localized compared to the
other (e.g., much heavier), it can serve as an effective potential barrier for
that mobile component. Near the limit of infinite localization, we map this to
a system of identical bosons in a double well. For realistic localization, the
backaction of the light species on the "barrier" atoms is explained--to lowest
order--in terms of an induced attraction between these. Even in equilibrium,
this may outweigh the bare intra-species interaction, leading to unexpected
correlated states. Remarkably, the backaction drastically affects the
inter-species dynamics, such as the tunneling of an attractively bound pair of
fermionized atoms.Comment: 10 pages, 3 figure
VR/Urban: SMSlingshot
In this paper we describe the concept and design objectives of VR/Urban's media intervention tool SMSlingshot, which was presented at the Riga White Night Arts Festival 2009 for the first time
Ground states of dipolar gases in quasi-1D ring traps
We compute the ground state of dipoles in a quasi-one-dimensional ring trap
using few-body techniques combined with analytic arguments. The effective
interaction between two dipoles depends on their center-of-mass coordinate and
can be tuned by varying the angle between dipoles and the plane of the ring.
For weak enough interactions, the state resembles a weakly interacting Fermi
gas or an (inhomogeneous) Lieb-Liniger gas. A mapping between the Lieb-Liniger
and the dipolar-gas parameters in and beyond the Born approximation is
established, and we discuss the effect of inhomogeneities based on a
local-density approximation. For strongly repulsive interactions, the system
exhibits crystal-like localization of the particles. Their inhomogeneous
distribution may be understood in terms of a simple few-body model as well as a
local-density approximation. In the case of partially attractive interactions,
clustered states form for strong enough coupling, and the dependence of the
state on particle number and orientation angle of the dipoles is discussed
analytically.Comment: 15 pages, 10 figure
Polarons and Molecules in a Two-Dimensional Fermi Gas
We study an impurity atom in a two-dimensional Fermi gas using variational
wave functions for (i) an impurity dressed by particle-hole excitations
(polaron) and (ii) a dimer consisting of the impurity and a majority atom. In
contrast to three dimensions, where similar calculations predict a sharp
transition to a dimer state with increasing interspecies attraction, we show
that the polaron ansatz always gives a lower energy. However, the exact
solution for a heavy impurity reveals that both a two-body bound state and
distortions of the Fermi sea are crucial. This reflects the importance of
particle-hole pairs in lower dimensions and makes simple variational
calculations unreliable. We show that the energy of an impurity gives important
information about its dressing cloud, for which both ans\"atze give inaccurate
results.Comment: 5 pages, 2 figures, minor change
Tunneling dynamics of few bosons in a double well
We study few-boson tunneling in a one-dimensional double well. As we pass
from weak interactions to the fermionization limit, the Rabi oscillations first
give way to highly delayed pair tunneling (for medium coupling), whereas for
very strong correlations multi-band Rabi oscillations emerge. All this is
explained on the basis of the exact few-body spectrum and without recourse to
the conventional two-mode approximation. Two-body correlations are found
essential to the understanding of the different tunnel mechanisms. The
investigation is complemented by discussing the effect of skewing the double
well, which offers the possibility to access specific tunnel resonancesComment: 10 pages, 8 figure
Correlations in Ultracold Trapped Few-Boson Systems: Transition from Condensation to Fermionization
We study the correlation properties of the ground states of few ultracold
bosons, trapped in double wells of varying barrier height in one dimension.
Extending previous results on the signature of the transition from a
Bose-condensed state via fragmentation to the hard-core limit, we provide a
deeper understanding of that transition by relating it to the loss of coherence
in the one-body density matrix and to the emerging long-range tail in the
momentum spectrum. These are accounted for in detail by discussing the natural
orbitals and their occupations. Our discussion is complemented by an analysis
of the two-body correlation function.Comment: 22 pages, 7 figure
Excitations of Few-Boson Systems in 1-D Harmonic and Double Wells
We examine the lowest excitations of one-dimensional few-boson systems
trapped in double wells of variable barrier height. Based on a numerically
exact multi-configurational method, we follow the whole pathway from the
non-interacting to the fermionization limit. It is shown how, in a purely
harmonic trap, the initially equidistant, degenerate levels are split up due to
interactions, but merge again for strong enough coupling. In a double well, the
low-lying spectrum is largely rearranged in the course of fermionization,
exhibiting level adhesion and (anti-)crossings. The evolution of the underlying
states is explained in analogy to the ground-state behavior. Our discussion is
complemented by illuminating the crossover from a single to a double well.Comment: 11 pages, 10 figure
Quantum dynamics of two bosons in an anharmonic trap: Collective vs internal excitations
This work deals with the effects of an anharmonic trap on an interacting
two-boson system in one dimension. Our primary focus is on the role of the
induced coupling between the center of mass and the relative motion as both
anharmonicity and the (repulsive) interaction strength are varied. The ground
state reveals a strong localization in the relative coordinate, counteracting
the tendency to fragment for stronger repulsion. To explore the quantum
dynamics, we study the system's response upon (i) exciting the harmonic ground
state by continuously switching on an additional anharmonicity, and (ii)
displacing the center of mass, this way triggering collective oscillations. The
interplay between collective and internal dynamics materializes in the collapse
of oscillations, which are explained in terms of few-mode models.Comment: 8 pages, 7 figure
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