566 research outputs found
Exciting Collective Oscillations in a Trapped 1D Gas
We report on the realization of a trapped one dimensional Bose gas and its
characterization by means of measuring its lowest lying collective excitations.
The quantum degenerate Bose gas is prepared in a 2D optical lattice and we find
the ratio of the frequencies of the lowest compressional (breathing) mode and
the dipole mode to be , in accordance with the
Lieb-Liniger and mean-field theory. For a thermal gas we measure
. By heating the quantum degenerate gas we have
studied the transition between the two regimes. For the lowest number of
particles attainable in the experiment the kinetic energy of the system is
similar to the interaction energy and we enter the strongly interacting regime.Comment: 4 pages, 4 figure
Creating topological interfaces and detecting chiral edge modes in a 2D optical lattice
We propose and analyze a general scheme to create chiral topological edge
modes within the bulk of two-dimensional engineered quantum systems. Our method
is based on the implementation of topological interfaces, designed within the
bulk of the system, where topologically-protected edge modes localize and
freely propagate in a unidirectional manner. This scheme is illustrated through
an optical-lattice realization of the Haldane model for cold atoms, where an
additional spatially-varying lattice potential induces distinct topological
phases in separated regions of space. We present two realistic experimental
configurations, which lead to linear and radial-symmetric topological
interfaces, which both allows one to significantly reduce the effects of
external confinement on topological edge properties. Furthermore, the
versatility of our method opens the possibility of tuning the position, the
localization length and the chirality of the edge modes, through simple
adjustments of the lattice potentials. In order to demonstrate the unique
detectability offered by engineered interfaces, we numerically investigate the
time-evolution of wave packets, indicating how topological transport
unambiguously manifests itself within the lattice. Finally, we analyze the
effects of disorder on the dynamics of chiral and non-chiral states present in
the system. Interestingly, engineered disorder is shown to provide a powerful
tool for the detection of topological edge modes in cold-atom setups.Comment: 18 pages, 21 figure
Exotic magnetic orders for high spin ultracold fermions
We study Hubbard models for ultracold bosonic or fermionic atoms loaded into
an optical lattice. The atoms carry a high spin , and interact on site
via strong repulsive Van der Waals forces. Making convenient rearrangements of
the interaction terms, and exploiting their symmetry properties, we derive low
energy effective models with nearest-neighbor interactions, and their
properties. We apply our method to , and 5/2 fermions on two-dimensional
square lattice at quarter, and 1/6 fillings, respectively, and investigate
mean-field equations for repulsive couplings. We find for fermions that
the plaquette state appearing in the highly symmetric SU(4) case does not
require fine tuning, and is stable in an extended region of the phase diagram.
This phase competes with an SU(2) flux state, that is always suppressed for
repulsive interactions in absence of external magnetic field. The SU(2) flux
state has, however, lower energy than the plaquette phase, and stabilizes in
the presence of weak applied magnetic field. For fermions a similar
SU(2) plaquette phase is found to be the ground state without external magnetic
field.Comment: final version, 6 pages, 4 figures, epl forma
Communications on Agricultural Research, Development, and Extension Teams
Domestically and internationally, agricultural research, development, and extension (ARD&E) programs are experiencing a resurgent interest in interdisciplinary collaboration as a more effective approach to enhancing farm productivity and human well-being
Observing the Profile of an Atom Laser Beam
We report on an investigation of the beam profile of an atom laser extracted
from a magnetically trapped Rb Bose-Einstein condensate. The transverse
momentum distribution is magnified by a curved mirror for matter waves and a
momentum resolution of 1/60 of a photon recoil is obtained. We find the
transverse momentum distribution to be determined by the mean-field potential
of the residing condensate, which leads to a non-smooth transverse density
distribution. Our experimental data are compared with a full 3D simulation of
the output coupling process and we find good agreement.Comment: 4 pages, 4 figure
The quantized Hall conductance of a single atomic wire: A proposal based on synthetic dimensions
We propose a method by which the quantization of the Hall conductance can be
directly measured in the transport of a one-dimensional atomic gas. Our
approach builds on two main ingredients: (1) a constriction optical potential,
which generates a mesoscopic channel connected to two reservoirs, and (2) a
time-periodic modulation of the channel, specifically designed to generate
motion along an additional synthetic dimension. This fictitious dimension is
spanned by the harmonic-oscillator modes associated with the tightly-confined
channel, and hence, the corresponding "lattice sites" are intimately related to
the energy of the system. We analyze the quantum transport properties of this
hybrid two-dimensional system, highlighting the appealing features offered by
the synthetic dimension. In particular, we demonstrate how the energetic nature
of the synthetic dimension, combined with the quasi-energy spectrum of the
periodically-driven channel, allows for the direct and unambiguous observation
of the quantized Hall effect in a two-reservoir geometry. Our work illustrates
how topological properties of matter can be accessed in a minimal
one-dimensional setup, with direct and practical experimental consequences.
1D Bose Gases in an Optical Lattice
We report on the study of the momentum distribution of a one-dimensional Bose
gas in an optical lattice. From the momentum distribution we extract the
condensed fraction of the gas and thereby measure the depletion of the
condensate and compare it with a theorical estimate. We have measured the
coherence length of the gas for systems with average occupation and
per lattice site.Comment: 4 pages, 3 figure
Time interval distributions of atoms in atomic beams
We report on the experimental investigation of two-particle correlations
between neutral atoms in a Hanbury Brown and Twiss experiment. Both an atom
laser beam and a pseudo-thermal atomic beam are extracted from a Bose-Einstein
condensate and the atom flux is measured with a single atom counter. We
determine the conditional and the unconditional detection probabilities for the
atoms in the beam and find good agreement with the theoretical predictions.Comment: 4 pages, 3 figure
Hybrid apparatus for Bose-Einstein condensation and cavity quantum electrodynamics: Single atom detection in quantum degenerate gases
We present and characterize an experimental system in which we achieve the
integration of an ultrahigh finesse optical cavity with a Bose-Einstein
condensate (BEC). The conceptually novel design of the apparatus for the
production of BECs features nested vacuum chambers and an in-vacuo magnetic
transport configuration. It grants large scale spatial access to the BEC for
samples and probes via a modular and exchangeable "science platform". We are
able to produce \87Rb condensates of five million atoms and to output couple
continuous atom lasers. The cavity is mounted on the science platform on top of
a vibration isolation system. The optical cavity works in the strong coupling
regime of cavity quantum electrodynamics and serves as a quantum optical
detector for single atoms. This system enables us to study atom optics on a
single particle level and to further develop the field of quantum atom optics.
We describe the technological modules and the operation of the combined BEC
cavity apparatus. Its performance is characterized by single atom detection
measurements for thermal and quantum degenerate atomic beams. The atom laser
provides a fast and controllable supply of atoms coupling with the cavity mode
and allows for an efficient study of atom field interactions in the strong
coupling regime. Moreover, the high detection efficiency for quantum degenerate
atoms distinguishes the cavity as a sensitive and weakly invasive probe for
cold atomic clouds
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