244 research outputs found
Magnetically tuned spin dynamics resonance
We present the experimental observation of a magnetically tuned resonance
phenomenon resulting from spin mixing dynamics of ultracold atomic gases. In
particular we study the magnetic field dependence of spin conversion in F=2
87Rb spinor condensates in the crossover from interaction dominated to
quadratic Zeeman dominated dynamics. We discuss the observed phenomenon in the
framework of spin dynamics as well as matter wave four wave mixing. Furthermore
we show that the validity range of the single mode approximation for spin
dynamics is significantly extended in the regime of high magnetic field
Measurement of a Mixed Spin Channel Feshbach Resonance in Rubidium 87
We report on the observation of a mixed spin channel Feshbach resonance at
the low magnetic field value of (9.09 +/- 0.01) G for a mixture of |2,-1> and
|1,+1> states in 87Rb. This mixture is important for applications of
multi-component BECs of 87Rb, e.g. in spin mixture physics and for quantum
entanglement. Values for position, height and width of the resonance are
reported and compared to a recent theoretical calculation of this resonance.Comment: 4 pages, 3 figures minor changes, actualized citation
Exact Solution of Strongly Interacting Quasi-One-Dimensional Spinor Bose Gases
We present an exact analytical solution of the fundamental system of
quasi-one-dimensional spin-1 bosons with infinite delta-repulsion. The
eigenfunctions are constructed from the wave functions of non-interacting
spinless fermions, based on Girardeau's Fermi-Bose mapping, and from the wave
functions of distinguishable spins. We show that the spinor bosons behave like
a compound of non-interacting spinless fermions and non-interacting
distinguishable spins. This duality is especially reflected in the spin
densities and the energy spectrum. We find that the momentum distribution of
the eigenstates depends on the symmetry of the spin function. Furthermore, we
discuss the splitting of the ground state multiplet in the regime of large but
finite repulsion.Comment: Revised to discuss large but finite interaction
Ultracold quantum gases in triangular optical lattices
Over the last years the exciting developments in the field of ultracold atoms
confined in optical lattices have led to numerous theoretical proposals devoted
to the quantum simulation of problems e.g. known from condensed matter physics.
Many of those ideas demand for experimental environments with non-cubic lattice
geometries. In this paper we report on the implementation of a versatile
three-beam lattice allowing for the generation of triangular as well as
hexagonal optical lattices. As an important step the superfluid-Mott insulator
(SF-MI) quantum phase transition has been observed and investigated in detail
in this lattice geometry for the first time. In addition to this we study the
physics of spinor Bose-Einstein condensates (BEC) in the presence of the
triangular optical lattice potential, especially spin changing dynamics across
the SF-MI transition. Our results suggest that below the SF-MI phase
transition, a well-established mean-field model describes the observed data
when renormalizing the spin-dependent interaction. Interestingly this opens new
perspectives for a lattice driven tuning of a spin dynamics resonance occurring
through the interplay of quadratic Zeeman effect and spin-dependent
interaction. We finally discuss further lattice configurations which can be
realized with our setup.Comment: 19 pages, 7 figure
Dynamics of dark solitons in elongated Bose-Einstein condensates
We find two types of moving dark soliton textures in elongated Bose-Einstein
condensates: non-stationary kinks and proper dark solitons. The former have a
curved notch region and rapidly decay by emitting phonons and/or proper dark
solitons. The proper moving solitons are characterized by a flat notch region
and we obtain the diagram of their dynamical stability. At finite temperatures
the dynamically stable solitons decay due to the thermodynamic instability. We
develop a theory of their dissipative dynamics and explain experimental data.Comment: ~ 5 pages, 1 figur
A Waveguide for Bose-Einstein Condensates
We report on the creation of Bose-Einstein condensates of Rb in a
specially designed hybrid, dipole and magnetic trap. This trap naturally allows
the coherent transfer of matter waves into a pure dipole potential waveguide
based on a doughnut beam. Specifically, we present studies of the coherence of
the ensemble in the hybrid trap and during the evolution in the waveguide by
means of an autocorrelation interferometer scheme. By monitoring the expansion
of the ensemble in the waveguide we observe a mean field dominated acceleration
on a much longer time scale than in the free 3D expansion. Both the
autocorrelation interference and the pure expansion measurements are in
excellent agreement with theoretical predictions of the ensemble dynamics
Localization of bosonic atoms by fermionic impurities in a 3d optical lattice
We observe a localized phase of ultracold bosonic quantum gases in a
3-dimensional optical lattice induced by a small contribution of fermionic
atoms acting as impurities in a Fermi-Bose quantum gas mixture. In particular
we study the dependence of this transition on the fermionic 40K impurity
concentration by a comparison to the corresponding superfluid to Mott insulator
transition in a pure bosonic 87Rb gas and find a significant shift in the
transition parameter. The observed shift is larger than expected based on a
mean-field argument, which is a strong indication that disorder-related effects
play a significant role.Comment: 4 pages, 4 figure
Do mixtures of bosonic and fermionic atoms adiabatically heat up in optical lattices?
Mixtures of bosonic and fermionic atoms in optical lattices provide a
promising arena to study strongly correlated systems. In experiments realizing
such mixtures in the quantum degenerate regime the temperature is a key
parameter. In this work, we investigate the intrinsic heating and cooling
effects due to an entropy-preserving raising of the optical lattice potential.
We analyze this process, identify the generic behavior valid for a wide range
of parameters, and discuss it quantitatively for the recent experiments with
87Rb and 40K atoms. In the absence of a lattice, we treat the bosons in the
Hartree-Fock-Bogoliubov-Popov-approximation, including the fermions in a
self-consistent mean field interaction. In the presence of the full
three-dimensional lattice, we use a strong coupling expansion. As a result of
the presence of the fermions, the temperature of the mixture after the lattice
ramp-up is always higher than for the pure bosonic case. This sheds light onto
a key point in the analysis of recent experiments.Comment: 5 pages, 3 figure
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