8,791 research outputs found
Optical Dipole Trapping beyond Rotating Wave Approximation: The case of Large Detuning
We show that the inclusion of counter-rotating terms, usually dropped in
evaluations of interaction of an electric dipole of a two level atom with the
electromagnetic field, leads to significant modifications of trapping potential
in the case of large detuning. The results are shown to be in excellent
numerical agreement with recent experimental findings, for the case of modes of
Laguerre-Gauss spatial profile.Comment: 13 pages, 2 figure
Design and fabrication of an autonomous rendezvous and docking sensor using off-the-shelf hardware
NASA Marshall Space Flight Center (MSFC) has developed and tested an engineering model of an automated rendezvous and docking sensor system composed of a video camera ringed with laser diodes at two wavelengths and a standard remote manipulator system target that has been modified with retro-reflective tape and 830 and 780 mm optical filters. TRW has provided additional engineering analysis, design, and manufacturing support, resulting in a robust, low cost, automated rendezvous and docking sensor design. We have addressed the issue of space qualification using off-the-shelf hardware components. We have also addressed the performance problems of increased signal to noise ratio, increased range, increased frame rate, graceful degradation through component redundancy, and improved range calibration. Next year, we will build a breadboard of this sensor. The phenomenology of the background scene of a target vehicle as viewed against earth and space backgrounds under various lighting conditions will be simulated using the TRW Dynamic Scene Generator Facility (DSGF). Solar illumination angles of the target vehicle and candidate docking target ranging from eclipse to full sun will be explored. The sensor will be transportable for testing at the MSFC Flight Robotics Laboratory (EB24) using the Dynamic Overhead Telerobotic Simulator (DOTS)
Exact Dynamics of Multicomponent Bose-Einstein Condensates in Optical Lattices in One, Two and Three Dimensions
Numerous exact solutions to the nonlinear mean-field equations of motion are
constructed for multicomponent Bose-Einstein condensates on one, two, and three
dimensional optical lattices. We find both stationary and nonstationary
solutions, which are given in closed form. Among these solutions are a
vortex-anti-vortex array on the square optical lattice and modes in which two
or more components slosh back and forth between neighboring potential wells. We
obtain a variety of solutions for multicomponent condensates on the simple
cubic lattice, including a solution in which one condensate is at rest and the
other flows in a complex three-dimensional array of intersecting vortex lines.
A number of physically important solutions are stable for a range of parameter
values, as we show by direct numerical integration of the equations of motion.Comment: 22 pages, 9 figure
Anharmonicity Induced Resonances for Ultracold Atoms and their Detection
When two atoms interact in the presence of an anharmonic potential, such as
an optical lattice, the center of mass motion cannot be separated from the
relative motion. In addition to generating a confinement-induced resonance (or
shifting the position of an existing Feshbach resonance), the external
potential changes the resonance picture qualitatively by introducing new
resonances where molecular excited center of mass states cross the scattering
threshold. We demonstrate the existence of these resonances, give their
quantitative characterization in an optical superlattice, and propose an
experimental scheme to detect them through controlled sweeping of the magnetic
field.Comment: 6 pages, 5 figures; expanded presentatio
Creation of a dipolar superfluid in optical lattices
We show that by loading a Bose-Einstein condensate (BEC) of two different
atomic species into an optical lattice, it is possible to achieve a
Mott-insulator phase with exactly one atom of each species per lattice site. A
subsequent photo-association leads to the formation of one heteronuclear
molecule with a large electric dipole moment, at each lattice site. The melting
of such dipolar Mott-insulator creates a dipolar superfluid, and eventually a
dipolar molecular BEC.Comment: 4 pages, 2 eps figure
Adaptive Horizon Model Predictive Control and Al'brekht's Method
A standard way of finding a feedback law that stabilizes a control system to
an operating point is to recast the problem as an infinite horizon optimal
control problem. If the optimal cost and the optmal feedback can be found on a
large domain around the operating point then a Lyapunov argument can be used to
verify the asymptotic stability of the closed loop dynamics. The problem with
this approach is that is usually very difficult to find the optimal cost and
the optmal feedback on a large domain for nonlinear problems with or without
constraints. Hence the increasing interest in Model Predictive Control (MPC).
In standard MPC a finite horizon optimal control problem is solved in real time
but just at the current state, the first control action is implimented, the
system evolves one time step and the process is repeated. A terminal cost and
terminal feedback found by Al'brekht's methoddefined in a neighborhood of the
operating point is used to shorten the horizon and thereby make the nonlinear
programs easier to solve because they have less decision variables. Adaptive
Horizon Model Predictive Control (AHMPC) is a scheme for varying the horizon
length of Model Predictive Control (MPC) as needed. Its goal is to achieve
stabilization with horizons as small as possible so that MPC methods can be
used on faster and/or more complicated dynamic processes.Comment: arXiv admin note: text overlap with arXiv:1602.0861
Aperiodic Ising Quantum Chains
Some years ago, Luck proposed a relevance criterion for the effect of
aperiodic disorder on the critical behaviour of ferromagnetic Ising systems. In
this article, we show how Luck's criterion can be derived within an exact
renormalisation scheme for Ising quantum chains with coupling constants
modulated according to substitution rules. Luck's conjectures for this case are
confirmed and refined. Among other outcomes, we give an exact formula for the
correlation length critical exponent for arbitrary two-letter substitution
sequences with marginal fluctuations of the coupling constants.Comment: 27 pages, LaTeX, 1 Postscript figure included, using epsf.sty and
amssymb.sty (one error corrected, some minor changes
Surface Properties of Aperiodic Ising Quantum Chains
We consider Ising quantum chains with quenched aperiodic disorder of the
coupling constants given through general substitution rules. The critical
scaling behaviour of several bulk and surface quantities is obtained by exact
real space renormalization.Comment: 4 pages, RevTex, reference update
Bichromatic Slowing of Metastable Helium
We examine two approaches for significantly extending the velocity range of
the optical bichromatic force (BCF), to make it useful for laser deceleration
of atomic and molecular beams. First, we present experimental results and
calculations for BCF deceleration of metastable helium using very large BCF
detunings, and discuss the limitations of this approach. We consider in detail
the constraints, both inherent and practical, that set the usable upper limit
of the BCF. We then show that a more promising approach is to utilize a BCF
profile with a relatively small velocity range in conjunction with chirped
Doppler shifts, to keep the force resonant with the atoms as they are slowed.
In an initial experimental test of this chirped BCF method, helium atoms are
slowed by m/s using a BCF profile with a velocity width of m/s. Straightforward scaling of the present results indicates that a
decelerator for He* capable of loading a magneto-optical trap (MOT) can yield a
brightness comparable to a much larger Zeeman slower.Comment: 11 pages, 9 figures. Published in Phys. Rev.
Saturation of Cs2 Photoassociation in an Optical Dipole Trap
We present studies of strong coupling in single-photon photoassociation of
cesium dimers using an optical dipole trap. A thermodynamic model of the trap
depletion dynamics is employed to extract absolute rate coefficents. From the
dependence of the rate coefficient on the photoassociation laser intensity, we
observe saturation of the photoassociation scattering probability at the
unitarity limit in quantitative agreement with the theoretical model by Bohn
and Julienne [Phys. Rev. A, 60, 414 (1999)]. Also the corresponding power
broadening of the resonance width is measured. We could not observe an
intensity dependent light shift in contrast to findings for lithium and
rubidium, which is attributed to the absence of a p or d-wave shape resonance
in cesium
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