2,260 research outputs found
Volcanic impact on stratospheric aerosol chemistry
Samples collected by the National Center for Atmospheric Research (NCAR) using the multiple-filter sampler on the U-2 were analyzed. The sampler is capable of exposing a number of 110 mm filters in sequence to ram air flow. Two types of filters, IPC cellulose and polystrene, were used, both of which have high blank levels for the trace elements determined. The levels of most trace elements in the stratosphere are so low under normal circumstances that none can be seen. Results from the eruption of Mt. St. Helens, a mystery cloud (probably volcanic in origin) in 1982, and the El Chichonal eruption in 1983 are discussed. To improve the collection of particles for chemical analysis, a new sampling system was developed for use on the U-2. The sampler consisted of an electrostatic collection of particles between 1 and 0.001 micron diameter dierectly onto electron microscopic grids, followed by a thermal precipitation for the smaller particles. The system was built and tested in the laboratory, but never flown on the U-2
Non-equilibrium dynamics of bosonic atoms in optical lattices: Decoherence of many-body states due to spontaneous emission
We analyze in detail the heating of bosonic atoms in an optical lattice due
to incoherent scattering of light from the lasers forming the lattice. Because
atoms scattered into higher bands do not thermalize on the timescale of typical
experiments, this process cannot be described by the total energy increase in
the system alone (which is determined by single-particle effects). The heating
instead involves an important interplay between the atomic physics of the
heating process and the many-body physics of the state. We characterize the
effects on many-body states for various system parameters, where we observe
important differences in the heating for strongly and weakly interacting
regimes, as well as a strong dependence on the sign of the laser detuning from
the excited atomic state. We compute heating rates and changes to
characteristic correlation functions based both on perturbation theory
calculations, and a time-dependent calculation of the dissipative many-body
dynamics. The latter is made possible for 1D systems by combining
time-dependent density matrix renormalization group (t-DMRG) methods with
quantum trajectory techniques.Comment: 17 pages, 14 figure
Measuring entanglement growth in quench dynamics of bosons in an optical lattice
We discuss a scheme to measure the many-body entanglement growth during
quench dynamics with bosonic atoms in optical lattices. By making use of a 1D
or 2D setup in which two copies of the same state are prepared, we show how
arbitrary order Renyi entropies can be extracted using tunnel-coupling between
the copies and measurement of the parity of on-site occupation numbers, as has
been performed in recent experiments. We illustrate these ideas for a
Superfluid-Mott insulator quench in the Bose-Hubbard model, and also for
hard-core bosons, and show that the scheme is robust against imperfections in
the measurements.Comment: 4+ pages plus supplementary materia
Quantum feedback cooling of a single trapped ion in front of a mirror
We develop a theory of quantum feedback cooling of a single ion trapped in
front of a mirror. By monitoring the motional sidebands of the light emitted
into the mirror mode we infer the position of the ion, and act back with an
appropriate force to cool the ion. We derive a feedback master equation along
the lines of the quantum feedback theory developed by Wiseman and Milburn,
which provides us with cooling times and final temperatures as a function of
feedback gain and various system parameters.Comment: 15 pages, 11 Figure
Spatial use and interaction of the raccoon dog (Nyctereutes procyonoides) and the red fox (Vulpes vulpes) in central Europe – competition or coexistence?
Drygala, F., Zoller, H
Mesoscopic Rydberg Gate based on Electromagnetically Induced Transparency
We demonstrate theoretically a parallelized C-NOT gate which allows to
entangle a mesoscopic ensemble of atoms with a single control atom in a single
step, with high fidelity and on a microsecond timescale. Our scheme relies on
the strong and long-ranged interaction between Rydberg atoms triggering
Electromagnetically Induced Transparency (EIT). By this we can robustly
implement a conditional transfer of all ensemble atoms among two logical
states, depending on the state of the control atom. We outline a many body
interferometer which allows a comparison of two many-body quantum states by
performing a measurement of the control atom.Comment: published versio
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