73 research outputs found
Wave mixing of optical pulses and Bose-Einstein condensates
We investigate theoretically the four-wave mixing of optical and matter waves
resulting from the scattering of a short light pulse off an atomic
Bose-Einstein condensate, as recently demonstrated by D. Schneble {\em et al.}
[ Science {\bf 300}, 475 (2003)]. We show that atomic ``pair production'' from
the condensate results in the generation of both forward- and
backward-propagating matter waves. These waves are characterized by different
phase-matching conditions, resulting in different angular distributions and
temporal evolutions.Comment: 4+\epsilon pages, 3 figure
Interspecies entanglement with impurity atoms in a lattice gas
The dynamics of impurity atoms introduced into bosonic gases in an optical lattice have generated a lot of recent interest, both in theory and experiment. We investigate to what extent measurements on either the impurity species or the majority species in these systems are affected by their interspecies entanglement. This arises naturally in the dynamics and plays an important role when we measure only one species. We explore the corresponding effects in strongly interacting regimes, using a combination of few-particle analytical calculations and density matrix renormalisation group methods in one dimension. We identify how the resulting effects on impurities can be used to probe the many-body states of the majority species, and separately ask how to enter regimes where this entanglement is small, so that the impurities can be used as probes that do not significantly affect the majority species. The results are accessible in current experiments, and provide important considerations for the measurement of complex systems with using few probe atoms
Improvement by laser quenching of an "atom diode": a one-way barrier for ultra-cold atoms
Different laser devices working as ``atom diodes'' or ``one-way barriers''
for ultra-cold atoms have been proposed recently. They transmit ground state
level atoms coming from one side, say from the left, but reflect them when they
come from the other side. We combine a previous model, consisting of the
stimulated Raman adiabatic passage (STIRAP) from the ground to an excited state
and a state-selective mirror potential, with a localized quenching laser which
produces spontaneous decay back to the ground state. This avoids backwards
motion, provides more control of the decay process and therefore a more compact
and useful device.Comment: 6 page
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
Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate
We investigate the effects of the atomic interaction in the Superradiant
Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned
laser beam. We show that for a homogeneous atomic sample the atomic interaction
has only a dispersive effect, whereas in the inhomogeneous case it may increase
the decay of the matter-wave grating.Comment: 12 pages, 4 figures, presented to the XII International Laser Physics
Workshop, August 24-29, Hamburg, to be published in Laser Physic
Single-electron population and depopulation of an isolated quantum dot using a surface-acoustic-wave pulse
We use a pulse of surface acoustic waves (SAWs) to control the electron population and depopulation of a quantum dot. The barriers between the dot and reservoirs are set high to isolate the dot. Within a time scale of similar to 100 s the dot can be set to a nonequilibrium charge state, where an empty (occupied) level stays below (above) the Fermi energy. A pulse containing a fixed number of SAW periods is sent through the dot, controllably changing the potential, and hence the tunneling probability, to add (remove) an electron to (from) the dot
Sequential superradiant scattering from atomic Bose-Einstein condensates
We theoretically discuss several aspects of sequential superradiant
scattering from atomic Bose-Einstein condensates. Our treatment is based on the
semiclassical description of the process in terms of the Maxwell-Schroedinger
equations for the coupled matter-wave and optical fields. First, we investigate
sequential scattering in the weak-pulse regime and work out the essential
mechanisms responsible for bringing about the characteristic fan-shaped
side-mode distribution patterns. Second, we discuss the transition between the
Kapitza-Dirac and Bragg regimes of sequential scattering in the strong-pulse
regime. Finally, we consider the situation where superradiance is initiated by
coherently populating an atomic side mode through Bragg diffraction, as in
studies of matter-wave amplification, and describe the effect on the sequential
scattering process.Comment: 9 pages, 4 figures. Submitted to Proceedings of LPHYS'06 worksho
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
Ocrelizumab exposure in relapsing–remitting multiple sclerosis: 10-year analysis of the phase 2 randomized clinical trial and its extension
Open-label extension (OLE) studies help inform long-term safety and efficacy of disease-modifying therapies in multiple sclerosis (MS). We report exploratory analyses from a phase 2 trial on the longest follow-up to date of ocrelizumab-treated patients with relapsing–remitting MS (RRMS). The primary treatment period (PTP) comprised four 24-week treatment cycles; participants were randomized to double-blind ocrelizumab (2000 mg or 600 mg), placebo, or interferon β-1a (open label) for one cycle, then dose-blinded ocrelizumab 1000 mg or 600 mg for the remaining cycles. The PTP was followed by consecutive assessed and unassessed treatment-free periods (TFPs) and then the OLE (ocrelizumab 600 mg every 24 weeks). Safety and efficacy were prospectively assessed. Of 220 participants randomized, 183 (84%) completed the PTP. After the TFP, 103 entered OLE (median OLE ocrelizumab exposure 6.5 years). Most common adverse events across all periods were infusion-related reactions. MRI activity, annualized relapse rate, and confirmed disability progression (CDP) rates remained low throughout. During the assessed TFP, there was a trend toward less and later B-cell repletion, and later CDP, for patients randomized to ocrelizumab; MRI activity was observed in 16.3% of patients, the earliest 24 weeks after the last ocrelizumab dose. This is the longest follow-up of ocrelizumab-treated patients with RRMS, with no new safety signals emerging during an observation period from 2008 to 2020. Results reinforce the sustained efficacy of long-term ocrelizumab. Reduced disease activity was maintained following interruption of 6-month dosing cycles, with no evidence of rebound
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