24,031 research outputs found
Field-free molecular orientation by THz laser pulses at high temperature
We investigate to which extend a THz laser pulse can be used to produce
field-free molecular orientation at high temperature. We consider laser pulses
that can be implemented with the state of the art technology and we show that
the efficiency of the control scheme crucially depends on the parameters of the
molecule. We analyze the temperature effects on molecular dynamics and we
demonstrate that, for some molecules, a noticeable orientation can be achieved
at high temperature.Comment: 13 pages, 7 figure
Photoassociation adiabatic passage of ultracold Rb atoms to form ultracold Rb_2 molecules
We theoretically explore photoassociation by Adiabatic Passage of two
colliding cold ^{85}Rb atoms in an atomic trap to form an ultracold Rb_2
molecule. We consider the incoherent thermal nature of the scattering process
in a trap and show that coherent manipulations of the atomic ensemble, such as
adiabatic passage, are feasible if performed within the coherence time window
dictated by the temperature, which is relatively long for cold atoms. We show
that a sequence of ~2*10^7 pulses of moderate intensities, each lasting ~750
ns, can photoassociate a large fraction of the atomic ensemble at temperature
of 100 microkelvin and density of 10^{11} atoms/cm^3. Use of multiple pulse
sequences makes it possible to populate the ground vibrational state. Employing
spontaneous decay from a selected excited state, one can accumulate the
molecules in a narrow distribution of vibrational states in the ground
electronic potential. Alternatively, by removing the created molecules from the
beam path between pulse sets, one can create a low-density ensemble of
molecules in their ground ro-vibrational state.Comment: RevTex, 23 pages, 9 figure
Overlapping resonances in the control of intramolecular vibrational redistribution
Coherent control of bound state processes via the interfering overlapping
resonances scenario [Christopher et al., J. Chem. Phys. 123, 064313 (2006)] is
developed to control intramolecular vibrational redistribution (IVR). The
approach is applied to the flow of population between bonds in a model of
chaotic OCS vibrational dynamics, showing the ability to significantly alter
the extent and rate of IVR by varying quantum interference contributions.Comment: 10 pages, 7 figure
Incomplete Photonic Bandgap as Inferred from the Speckle Pattern of Scattered Light Waves
Motivated by recent experiments on intensity correlations of the waves
transmitted through disordered media, we demonstrate that the speckle pattern
from disordered photonic crystal with incomplete band-gap represents a
sensitive tool for determination the stop-band width. We establish the
quantitative relation between this width and the {\em angualar anisotropy} of
the intensity correlation function.Comment: 6 pages, 3 figure
Automatic structures, rational growth and geometrically finite hyperbolic groups
We show that the set of equivalence classes of synchronously
automatic structures on a geometrically finite hyperbolic group is dense in
the product of the sets over all maximal parabolic subgroups . The
set of equivalence classes of biautomatic structures on is
isomorphic to the product of the sets over the cusps (conjugacy
classes of maximal parabolic subgroups) of . Each maximal parabolic is a
virtually abelian group, so and were computed in ``Equivalent
automatic structures and their boundaries'' by M.Shapiro and W.Neumann, Intern.
J. of Alg. Comp. 2 (1992) We show that any geometrically finite hyperbolic
group has a generating set for which the full language of geodesics for is
regular. Moreover, the growth function of with respect to this generating
set is rational. We also determine which automatic structures on such a group
are equivalent to geodesic ones. Not all are, though all biautomatic structures
are.Comment: Plain Tex, 26 pages, no figure
Generic Quantum Ratchet Accelerator with Full Classical Chaos
A simple model of quantum ratchet transport that can generate unbounded
linear acceleration of the quantum ratchet current is proposed, with the
underlying classical dynamics fully chaotic. The results demonstrate that
generic acceleration of quantum ratchet transport can occur with any type of
classical phase space structure. The quantum ratchet transport with full
classical chaos is also shown to be very robust to noise due to the large
linear acceleration afforded by the quantum dynamics. One possible experiment
allowing observation of these predictions is suggested.Comment: 4 pages, 4 figure
Empowerment Through Risk-Related Information: EPA's Risk Screening Environmental Indicators Project
Implementing Quantum Gates by Optimal Control with Doubly Exponential Convergence
We introduce a novel algorithm for the task of coherently controlling a
quantum mechanical system to implement any chosen unitary dynamics. It performs
faster than existing state of the art methods by one to three orders of
magnitude (depending on which one we compare to), particularly for quantum
information processing purposes. This substantially enhances the ability to
both study the control capabilities of physical systems within their coherence
times, and constrain solutions for control tasks to lie within experimentally
feasible regions. Natural extensions of the algorithm are also discussed.Comment: 4+2 figures; to appear in PR
The Equation of State of Dense Matter : from Nuclear Collisions to Neutron Stars
The Equation of State (EoS) of dense matter represents a central issue in the
study of compact astrophysical objects and heavy ion reactions at intermediate
and relativistic energies. We have derived a nuclear EoS with nucleons and
hyperons within the Brueckner-Hartree-Fock approach, and joined it with quark
matter EoS. For that, we have employed the MIT bag model, as well as the
Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and found that
the NS maximum masses are not larger than 1.7 solar masses. A comparison with
available data supports the idea that dense matter EoS should be soft at low
density and quite stiff at high density.Comment: 8 pages, 5 figures, invited talk given at NPA3, Dresden, March 200
Importance of cooling in triggering the collapse of hypermassive neutron stars
The inspiral and merger of a binary neutron star (NSNS) can lead to the
formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal
pressure due to neutrino cooling and/or centrifugal support due to
gravitational wave (GW) emission, and/or magnetic breaking of differential
rotation it will collapse to a black hole. To assess the importance of
shock-induced thermal pressure and cooling, we adopt an idealized equation of
state and perform NSNS simulations in full GR through late inspiral, merger,
and HMNS formation, accounting for cooling. We show that thermal pressure
contributes significantly to the support of the HMNS against collapse and that
thermal cooling accelerates its "delayed" collapse. Our simulations demonstrate
explicitly that cooling can induce the catastrophic collapse of a hot
hypermassive neutron star formed following the merger of binary neutron stars.
Thus, cooling physics is important to include in NSNS merger calculations to
accurately determine the lifetime of the HMNS remnant and to extract
information about the NS equation of state, cooling mechanisms, bar
instabilities and B-fields from the GWs emitted during the transient phase
prior to BH formation.Comment: 13 pages, 7 figures, matches published versio
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