139 research outputs found
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
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
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
Self-trapping of impurities in Bose-Einstein condensates: Strong attractive and repulsive coupling
We study the interaction-induced localization -- the so-called self-trapping
-- of a neutral impurity atom immersed in a homogeneous Bose-Einstein
condensate (BEC). Based on a Hartree description of the BEC we show that --
unlike repulsive impurities -- attractive impurities have a singular ground
state in 3d and shrink to a point-like state in 2d as the coupling approaches a
critical value. Moreover, we find that the density of the BEC increases
markedly in the vicinity of attractive impurities in 1d and 2d, which strongly
enhances inelastic collisions between atoms in the BEC. These collisions result
in a loss of BEC atoms and possibly of the localized impurity itself.Comment: 7 pages, 5 figure
Evolution of a spinor condensate: coherent dynamics, dephasing and revivals
We present measurements and a theoretical model for the interplay of spin
dependent interactions and external magnetic fields in atomic spinor
condensates. We highlight general features like quadratic Zeeman dephasing and
its influence on coherent spin mixing processes by focusing on a specific
coherent superposition state in a F=1 Rb Bose-Einstein condensate. In
particular, we observe the transition from coherent spinor oscillations to
thermal equilibration
Phase Fluctuations in Bose-Einstein Condensates
We demonstrate the existence of phase fluctuations in elongated Bose-Einstein
Condensates (BECs) and study the dependence of those fluctuations on the system
parameters. A strong dependence on temperature, atom number, and trapping
geometry is observed. Phase fluctuations directly affect the coherence
properties of BECs. In particular, we observe instances where the phase
coherence length is significantly smaller than the condensate size. Our method
of detecting phase fluctuations is based on their transformation into density
modulations after ballistic expansion. An analytic theory describing this
transformation is developed.Comment: 11 pages, 7 figure
Characterization and control of phase fluctuations in elongated Bose-Einstein condensates
Quasi one dimensional Bose-Einstein condensates (BECs) in elongated traps
exhibit significant phase fluctuations even at very low temperatures. We
present recent experimental results on the dynamic transformation of phase
fluctuations into density modulations during time-of-flight and show the
excellent quantitative agreement with the theoretical prediction. In addition
we confirm that under our experimental conditions, in the magnetic trap density
modulations are strongly suppressed even when the phase fluctuates. The paper
also discusses our theoretical results on control of the condensate phase by
employing a time-dependent perturbation. Our results set important limitations
on future applications of BEC in precision atom interferometry and atom optics,
but at the same time suggest pathways to overcome these limitations.Comment: 9 pages, 7 figure
Precision measurement and compensation of optical Stark shifts for an ion-trap quantum processor
Using optical Ramsey interferometry, we precisely measure the laser-induced
AC-stark shift on the -- "quantum bit" transition near 729
nm in a single trapped Ca ion. We cancel this shift using an
additional laser field. This technique is of particular importance for the
implementation of quantum information processing with cold trapped ions. As a
simple application we measure the atomic phase evolution during a rotation of the quantum bit.Comment: 4 pages, 4 figure
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