38 research outputs found
Inelastic chaotic scattering on a Bose-Einstein condensate
We devise a microscopic scattering approach to probe the excitation spectrum
of a Bose-Einstein condensate. We show that the experimentally accessible
scattering cross section exhibits universal Ericson fluctuations, with
characteristic properties rooted in the underlying classical field equations.Comment: 11 pages, 5 figure
Versatile transporter apparatus for experiments with optically trapped Bose-Einstein condensates
We describe a versatile and simple scheme for producing magnetically and
optically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil
transporter apparatus. The apparatus features a TOP trap that incorporates the
movable quadrupole coils used for magneto-optical trapping and long-distance
magnetic transport of atomic clouds. As a stand-alone device, this trap allows
for the stable production of condensates containing up to one million atoms. In
combination with an optical dipole trap, the TOP trap acts as a funnel for
efficient loading, after which the quadrupole coils can be retracted, thereby
maximizing optical access. The robustness of this scheme is illustrated by
realizing the superfluid-to-Mott insulator transition in a three-dimensional
optical lattice
Thermometry with spin-dependent lattices
We propose a method for measuring the temperature of strongly correlated
phases of ultracold atom gases confined in spin-dependent optical lattices. In
this technique, a small number of "impurity" atoms--trapped in a state that
does not experience the lattice potential--are in thermal contact with atoms
bound to the lattice. The impurity serves as a thermometer for the system
because its temperature can be straightforwardly measured using time-of-flight
expansion velocity. This technique may be useful for resolving many open
questions regarding thermalization in these isolated systems. We discuss the
theory behind this method and demonstrate proof-of-principle experiments,
including the first realization of a 3D spin-dependent lattice in the strongly
correlated regime.Comment: 22 pages, 8 figures v2: Several references added; Section on heating
rates updated to include dipole fluctuation terms; Section added on the
limitations of the proposed method. To appear in New Journal of Physic
Interaction and filling induced quantum phases of dual Mott insulators of bosons and fermions
Many-body effects are at the very heart of diverse phenomena found in
condensed-matter physics. One striking example is the Mott insulator phase
where conductivity is suppressed as a result of a strong repulsive interaction.
Advances in cold atom physics have led to the realization of the Mott
insulating phases of atoms in an optical lattice, mimicking the corresponding
condensed matter systems. Here, we explore an exotic strongly-correlated system
of Interacting Dual Mott Insulators of bosons and fermions. We reveal that an
inter-species interaction between bosons and fermions drastically modifies each
Mott insulator, causing effects that include melting, generation of composite
particles, an anti-correlated phase, and complete phase-separation. Comparisons
between the experimental results and numerical simulations indicate intrinsic
adiabatic heating and cooling for the attractively and repulsively interacting
dual Mott Insulators, respectively
The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting
more than 1 year and culminating in spring 2005. The maximum brightness
detected was R = 12.0, which represents the most luminous quasar state thus far
observed (M_B ~ -31.4). In order to follow the emission behaviour of the source
in detail, a large multiwavelength campaign was organized by the Whole Earth
Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was
performed in several bands. ToO pointings by the Chandra and INTEGRAL
satellites provided additional information at high energies in May 2005. The
historical radio and optical light curves show different behaviours. Until
about 2001.0 only moderate variability was present in the optical regime, while
prominent and long-lasting radio outbursts were visible at the various radio
frequencies, with higher-frequency variations preceding the lower-frequency
ones. After that date, the optical activity increased and the radio flux is
less variable. This suggests that the optical and radio emissions come from two
separate and misaligned jet regions, with the inner optical one acquiring a
smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index
behaviour (generally redder-when-brighter) during the outburst suggests the
presence of a luminous accretion disc. A huge mm outburst followed the optical
one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux
started to increase in early 2005 and reached a maximum at the end of our
observing period (end of September 2005). VLBA observations at 43 GHz during
the summer confirm theComment: 7 pages, 4 figures, to be published in A&
Interactions and Mobility Edges: Observing the Generalized Aubry-Andre Model
Using synthetic lattices of laser-coupled atomic momentum modes, we experimentally realize a recently proposed family of nearest-neighbor tight-binding models having quasiperiodic site energy modulation that host an exact mobility edge protected by a duality symmetry. These one-dimensional tight-binding models can be viewed as a generalization of the well-known Aubry-Andre model, with an energy-dependent self-duality condition that constitutes an analytical mobility edge relation. By adiabatically preparing low and high energy eigenstates of this model system and performing microscopic measurements of their participation ratio, we track the evolution of the mobility edge as the energy-dependent density of states is modified by the model's tuning parameter. Our results show strong deviations from single-particle predictions, consistent with attractive interactions causing both enhanced localization of the lowest energy state due to self-trapping and inhibited localization of high energy states due to screening. This study paves the way for quantitative studies of interaction effects on self-duality induced mobility edges
Observation of the topological Anderson insulator in disordered atomic wires
Topology and disorder have a rich combined influence on quantum transport. To probe their interplay, we synthesized one-dimensional chiral symmetric wires with controllable disorder via spectroscopic Hamiltonian engineering, based on the laser-driven coupling of discrete momentum states of ultracold atoms. Measuring the bulk evolution of a topological indicator after a sudden quench, we observed the topological Anderson insulator phase, in which added disorder drives the band structure of a wire from topologically trivial to nontrivial. In addition, we observed the robustness of topologically nontrivial wires to weak disorder and measured the transition to a trivial phase in the presence of strong disorder. Atomic interactions in this quantum simulation platform may enable realizations of strongly interacting topological fluids