678 research outputs found
The steady state quantum statistics of a non-Markovian atom laser
We present a fully quantum mechanical treatment of a single-mode atomic
cavity with a pumping mechanism and an output coupling to a continuum of
external modes. This system is a schematic description of an atom laser. In the
dilute limit where atom-atom interactions are negligible, we have been able to
solve this model without making the Born and Markov approximations. When
coupling into free space, it is shown that for reasonable parameters there is a
bound state which does not disperse, which means that there is no steady state.
This bound state does not exist when gravity is included, and in that case the
system reaches a steady state. We develop equations of motion for the two-time
correlation in the presence of pumping and gravity in the output modes. We then
calculate the steady-state output energy flux from the laser.Comment: 14 pages (twocloumn), 6 figure
Effectiveness of new agri-environment schemes in conserving arable plants in intensively farmed landscapes
Exact quantum jump approach to open systems in Bosonic and spin baths
A general method is developed which enables the exact treatment of the
non-Markovian quantum dynamics of open systems through a Monte Carlo simulation
technique. The method is based on a stochastic formulation of the von Neumann
equation of the composite system and employs a pair of product states following
a Markovian random jump process. The performance of the method is illustrated
by means of stochastic simulations of the dynamics of open systems interacting
with a Bosonic reservoir at zero temperature and with a spin bath in the strong
coupling regime.Comment: 4 pages, 2 figure
Effects of interatomic collisions on atom laser outcoupling
We present a computational approach to the outcoupling in a simple
one-dimensional atom laser model, the objective being to circumvent
mathematical difficulties arising from the breakdown of the Born and Markov
approximations. The approach relies on the discretization of the continuum
representing the reservoir of output modes, which allows the treatment of
arbitrary forms of outcoupling as well as the incorporation of non-linear terms
in the Hamiltonian, associated with interatomic collisions. By considering a
single-mode trapped condensate, we study the influence of elastic collisions
between trapped and free atoms on the quasi steady-state population of the
trap, as well as the energy distribution and the coherence of the outcoupled
atoms.Comment: 25 pages, 11 figures, to appear in J. Phys.
Quantum dynamical theory for squeezing the output of a Bose-Einstein condensate
A linear quantum dynamical theory for squeezing the output of the trapped
Bose-Einstein condensate is presented with the Bogoliubov approximation. We
observe that the non-classical properties, such as sub-Poisson distribution and
quadrature squeezing effect, mutually oscillate between the quantum states of
the applied optical field and the resulting atom laser beam with time. In
particular, it is shown that an initially squeezed optical field will lead to
squeezing in the outcoupled atomic beam at later times.Comment: 6 pages, Latex file, Phys.Rev.A 63(2001)1560
Output of a pulsed atom laser
We study the output properties of a pulsed atom laser consisting of an
interacting Bose-Einstein condensate (BEC) in a magnetic trap and an additional
rf field transferring atoms to an untrapped Zeeman sublevel. For weak output
coupling we calculate the dynamics of the decaying condensate population, of
its chemical potential and the velocity of the output atoms analytically.Comment: 4 pages, RevTeX. Full ps file available on
http://mpqibmr1.mpq.mpg.de:5000/~man
Theory of output coupling for trapped fermionic atoms
We develop a dynamic theory of output coupling, for fermionic atoms initially
confined in a magnetic trap. We consider an exactly soluble one-dimensional
model, with a spatially localized delta-type coupling between the atoms in the
trap and a continuum of free-particle external modes. Two important special
cases are considered for the confinement potential: the infinite box and the
harmonic oscillator. We establish that in both cases a bound state of the
coupled system appears for any value of the coupling constant, implying that
the trap population does not vanish in the infinite-time limit. For weak
coupling, the energy spectrum of the outgoing beam exhibits peaks corresponding
to the initially occupied energy levels in the trap; the height of these peaks
increases with the energy. As the coupling gets stronger, the energy spectrum
is displaced towards dressed energies of the fermions in the trap. The
corresponding dressed states result from the coupling between the unperturbed
fermionic states in the trap, mediated by the coupling between these states and
the continuum. In the strong-coupling limit, there is a reinforcement of the
lowest-energy dressed mode, which contributes to the energy spectrum of the
outgoing beam more strongly than the other modes. This effect is especially
pronounced for the one-dimensional box, which indicates that the efficiency of
the mode-reinforcement mechanism depends on the steepness of the confinement
potential. In this case, a quasi-monochromatic anti-bunched atomic beam is
obtained. Results for a bosonic sample are also shown for comparison.Comment: 16 pages, 7 figures, added discussion on time-dependent spectral
distribution and corresponding figur
Bridging the lesson distribution gap
Paper presented at The 17th International Joint Conference on Artificial Intelligence, IJCAI 2001, Seattle, WA: pp. 987-992.Many organizations employ lessons learned (LL)
processes to collect, analyze, store, and distribute,
validated experiential knowledge (lessons) of their
members that, when reused, can substantially improve
organizational decision processes. Unfortunately,
deployed LL systems do not facilitate lesson reuse and
fail to bring lessons to the attention of the users when
and where they are needed and applicable (i.e., they
fail to bridge the lesson distribution gap). Our
approach for solving this problem, named monitored
distribution, tightly integrates lesson distribution with
these decision processes. We describe a case-based
implementation of monitored distribution (ALDS) in a
plan authoring tool suite (HICAP). We evaluate its
utility in a simulated military planning domain. Our
results show that monitored distribution can
significantly improve plan evaluation measures for this
domain
Bridging the lesson distribution gap
Paper presented at The 17th International Joint Conference on Artificial Intelligence, IJCAI 2001, Seattle, WA: pp. 987-992.Many organizations employ lessons learned (LL)
processes to collect, analyze, store, and distribute,
validated experiential knowledge (lessons) of their
members that, when reused, can substantially improve
organizational decision processes. Unfortunately,
deployed LL systems do not facilitate lesson reuse and
fail to bring lessons to the attention of the users when
and where they are needed and applicable (i.e., they
fail to bridge the lesson distribution gap). Our
approach for solving this problem, named monitored
distribution, tightly integrates lesson distribution with
these decision processes. We describe a case-based
implementation of monitored distribution (ALDS) in a
plan authoring tool suite (HICAP). We evaluate its
utility in a simulated military planning domain. Our
results show that monitored distribution can
significantly improve plan evaluation measures for this
domain
Optical Confinement of a Bose-Einstein Condensate
Bose-Einstein condensates of sodium atoms have been confined in an optical
dipole trap using a single focused infrared laser beam. This eliminates the
restrictions of magnetic traps for further studies of atom lasers and
Bose-Einstein condensates. More than five million condensed atoms were
transferred into the optical trap. Densities of up to of Bose condensed atoms were obtained, allowing for a measurement of
the three-body decay rate constant for sodium condensates as . At lower densities, the observed 1/e
lifetime was more than 10 sec. Simultaneous confinement of Bose-Einstein
condensates in several hyperfine states was demonstrated.Comment: 5 pages, 4 figure
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