263 research outputs found
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
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
Spin waves in a Bose Ferromagnet
It is shown that the ferromagnetic transition takes place always above
Bose-Einstein condensation in ferromagnetically coupled spinor Bose gases. We
describe the Bose ferromagnet within Ginzburg-Landau theory by a "two-fluid"
model below Bose-Einstein condensation. Both the Bose condensate and the normal
phase are spontaneously magnetized. As a main result we show that spin waves in
the two fluids are coupled together so as to produce only one mixed spin-wave
mode in the coexisting state. The long wavelength spectrum is quadratic in the
wave vector , consistent with usual ferromagnetism theory, and the
spin-wave stiffness coefficient includes contributions from both the two
phases, implying the "two-fluid" feature of the system. can show a sharp
bend at the Bose-Einstein condensation temperature.Comment: 4 pages, 1 figur
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
Second Order Correlation Function of a Phase Fluctuating Bose-Einstein Condensate
The coherence properties of phase fluctuating Bose-Einstein condensates are
studied both theoretically and experimentally. We derive a general expression
for the N-particle correlation function of a condensed Bose gas in a highly
elongated trapping potential. The second order correlation function is analyzed
in detail and an interferometric method to directly measure it is discussed and
experimentally implemented. Using a Bragg diffraction interferometer, we
measure intensity correlations in the interference pattern generated by two
spatially displaced copies of a parent condensate. Our experiment demonstrates
how to characterize the second order correlation function of a highly elongated
condensate and to measure its phase coherence length.Comment: 22 pages, 5 figure
Bose-Einstein condensation at constant temperature
We present a novel experimental approach to Bose-Einstein condensation by
increasing the particle number of the system at almost constant temperature. In
particular the emergence of a new condensate is observed in multi-component F=1
spinor condensates of 87-Rb. Furthermore we develop a simple rate-equation
model for multi-component BEC thermodynamics at finite temperature which well
reproduces the measured effects.Comment: 4 pages, 3 figures, RevTe
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