8,811 research outputs found
Disentanglement and Decoherence by Open System Dynamics
The destruction of quantum interference, decoherence, and the destruction of
entanglement both appear to occur under the same circumstances. To address the
connection between these two phenomena, we consider the evolution of arbitrary
initial states of a two-particle system under open system dynamics described by
a class of master equations which produce decoherence of each particle. We show
that all initial states become separable after a finite time, and we produce
the explicit form of the separated state. The result extends and amplifies an
earlier result of Di\'osi. We illustrate the general result by considering the
case in which the initial state is an EPR state (in which both the positions
and momenta of a particle pair are perfectly correlated). This example clearly
illustrates how the spreading out in phase space produced by the environment
leads to certain disentanglement conditions becoming satisfied.Comment: 15 Page
Disentanglement by Dissipative Open System Dynamics
This paper investigates disentanglement as a result of evolution according to
a class of master equations which include dissipation and interparticle
interactions. Generalizing an earlier result of Di\'{o}si, the time taken for
complete disentanglement is calculated (i.e. for disentanglement from any other
system). The dynamics of two harmonically coupled oscillators is solved in
order to study the competing effects of environmental noise and interparticle
coupling on disentanglement. An argument based on separability conditions for
gaussian states is used to arrive at a set of conditions on the couplings
sufficient for all initial states to disentangle for good after a finite time.Comment: Paper in conjunction with and following on from P.J. Dodd and J.J.
Halliwell: quant-ph/031206
Recommended from our members
Effect of side chains on the dielectric properties of alkyl esters derived from palm kernel oil
Alkyl ester derivatives were synthesized from laboratory purified palm kernel oil. The steps in the synthesis involved transesterification of palm kernel oil to produce a methyl ester, followed by epoxidation and then the grafting of side chains by esterification with propionic and butyric anhydride. The dielectric and thermal properties of the ester derivatives were analyzed and compared with the methyl ester. The melting point of the ester derivatives were found to reduce with side chain attachment and antioxidant improved its thermal stability. The dielectric loss was dominated by mobile charged particles and the chemical modification appeared to increase the rate at which electric double layer was formed at the electrode-liquid interface. The esters possessed excellent breakdown strengths suggesting that the processing to optimize their physical properties did not have a negative influence on their electrical breakdown strength. This product may prove useful as an insulation fluid in Electrical Power Transformers
Collective excitations of atomic Bose-Einstein condensates
We apply linear-response analysis of the Gross-Pitaevskii equation to obtain
the excitation frequencies of a Bose-Einstein condensate confined in a
time-averaged orbiting potential trap. Our calculated values are in excellent
agreement with those observed in a recent experiment.Comment: 11 pages, 2 Postscript figures, uses psbox.tex for automatic figure
inclusion. More info at http://amo.phy.gasou.edu/bec.htm
Two point correlations of a trapped interacting Bose gas at finite temperature
We develop a computationally tractable method for calculating correlation
functions of the finite temperature trapped Bose gas that includes the effects
of s-wave interactions. Our approach uses a classical field method to model the
low energy modes and treats the high energy modes using a Hartree-Fock
description. We present results of first and second order correlation
functions, in position and momentum space, for an experimentally realistic
system in the temperature range of to . We also characterize
the spatial coherence length of the system. Our theory should be applicable in
the critical region where experiments are now able to measure first and second
order correlations.Comment: 9 pages, 4 figure
Long-range sound-mediated dark soliton interactions in trapped atomic condensates
A long-range soliton interaction is discussed whereby two or more dark
solitons interact in an inhomogeneous atomic condensate, modifying their
respective dynamics via the exchange of sound waves without ever coming into
direct contact. An idealized double well geometry is shown to yield perfect
energy transfer and complete periodic identity reversal of the two solitons.
Two experimentally relevant geometries are analyzed which should enable the
observation of this long-range interaction
Vortices in attractive Bose-Einstein condensates in two dimensions
The form and stability of quantum vortices in Bose-Einstein condensates with
attractive atomic interactions is elucidated. They appear as ring bright
solitons, and are a generalization of the Townes soliton to nonzero winding
number . An infinite sequence of radially excited stationary states appear
for each value of , which are characterized by concentric matter-wave rings
separated by nodes, in contrast to repulsive condensates, where no such set of
states exists. It is shown that robustly stable as well as unstable regimes may
be achieved in confined geometries, thereby suggesting that vortices and their
radial excited states can be observed in experiments on attractive condensates
in two dimensions.Comment: 4 pages, 3 figure
Formal Verification of a Gain Scheduling Control Scheme
Gain scheduling is a commonly used closed-loop control approach for safety critical non-linear systems, such as commercial gas turbine engines. It is preferred over more advanced control strategies due to a known route to certification. Nonetheless, the stability of the system is hard to prove analytically, and consequently, safety and airworthiness is achieved by burdensome extensive testing. Model checking can aid in bringing down development costs of such a control system and simultaneously improve safety by providing guarantees on properties of embedded control systems. Due to model-checking exhaustive verification capabilities, it has long been recognised that coverage and error-detection rate can be increased compared to traditional testing methods. However, the statespace explosion is still a major computational limitation when applying model-checking to verify dynamic system behaviour. A practical methodology to incrementally design and formally verify control system requirements for a gain scheduling scheme is demonstrated in this paper, overcoming the computational constraints traditionally imposed by model checking. In this manner, the gain-scheduled controller can be efficiently and safely generated with the aid of the model checker
Gas Purity effect on GEM Performance in He and Ne at Low Temperatures
The performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne, He+H2
and Ne+H2 was studied at temperatures in the range of 3-293 K. This paper
reports on previously published measurements and additional studies on the
effects of the purity of the gases in which the GEM performance is evaluated.
In He, at temperatures between 77 and 293 K, triple-GEM structures operate at
rather high gains, exceeding 1000. There is an indication that this high gain
is achieved through the Penning effect as a result of impurities in the gas. At
lower temperatures the gain-voltage characteristics are significantly modified
probably due to the freeze-out of these impurities. Double-GEM and single-GEM
structures can operate down to 3 K at gains reaching only several tens at a gas
density of about 0.5 g/l; at higher densities the maximum gain drops further.
In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in
Ne at low temperatures can be re-established in Penning mixtures of Ne+H2: very
high gains, exceeding 104, have been obtained in these mixtures at 30-77 K, at
a density of 9.2 g/l which corresponds to saturated Ne vapor density at 27 K.
The addition of small amounts of H2 in He also re-establishes large GEM gains
above 30 K but no gain was observed in He+H2 at 4 K and a density of 1.7 g/l
(corresponding to roughly one-tenth of the saturated vapor density). These
studies are, in part, being pursued in the development of two-phase He and Ne
detectors for solar neutrino detection.Comment: 4 pages, 7 figure
- …