2,499 research outputs found
Two-mode squeezed vacuum state coupled to the common thermal reservoir
Entangled states play a crucial role in quantum information protocols, thus
the dynamical behavior of entanglement is of a great importance. In this paper
we consider a two-mode squeezed vacuum state coupled to one thermal reservoir
as a model of an entangled state embedded in an environment. As a criterion for
entanglement we use a continuous-variable equivalent of the Peres-Horodecki
criterion, namely the Simon criterion. To quantify entanglement we use the
logarithmic negativity. We derive a condition, which assures that the state
remains entangled in spite of the interaction with the reservoir. Moreover for
the case of interaction with vacuum as an environment we show that a state of
interest after intinitely long interaction is not only entangled, but also
pure. For comparison we also consider a model in which each of both modes is
coupled to its own reservoir.Comment: replaced with version published in J. Phys.
Non-sequential double ionization of molecules
Double ionization of diatomic molecules by short linearly polarized laser
pulses is analyzed. We consider the final stage of the ionization process, that
is the decay of a highly excited two electron molecule, which is formed after
re-scattering. The saddles of the effective adiabatic potential energy close to
which simultaneous escape of electrons takes place are identified. Numerical
simulations of the ionization of molecules show that the process can be
dominated by either sequential or non-sequential events.
In order to increase the ratio of non-sequential to sequential ionizations
very short laser pulses should be applied.Comment: 7 pages, 7 figures, submitted to PR
Double ionization of a three-electron atom: Spin correlation effects
We study the effects of spin degrees of freedom and wave function symmetries
on double ionization in three-electron systems. Each electron is assigned one
spatial degree of freedom. The resulting three-dimensional Schr\"odinger
equation is integrated numerically using grid-based Fourier transforms. We
reveal three-electron effects on the double ionization yield by comparing
signals for different ionization channels. We explain our findings by the
existence of fundamental differences between three-electronic and truly
two-electronic spin-resolved ionization schemes. We find, for instance, that
double ionization from a three-electron system is dominated by electrons that
have the opposite spin
Mean field dynamics of superfluid-insulator phase transition in a gas of ultra cold atoms
A large scale dynamical simulation of the superfluid to Mott insulator
transition in the gas of ultra cold atoms placed in an optical lattice is
performed using the time dependent Gutzwiller mean field approach. This
approximate treatment allows us to take into account most of the details of the
recent experiment [Nature 415, 39 (2002)] where by changing the depth of the
lattice potential an adiabatic transition from a superfluid to a Mott insulator
state has been reported. Our simulations reveal a significant excitation of the
system with a transition to insulator in restricted regions of the trap.Comment: final version, correct Fig.7 (the published version contains wrong
fig.7 by mistake
Non-sequential double ionization of molecules in a strong laser field
We consider the final stage of double ionization of molecules by
short linearly polarized laser pulses. The saddles of the effective adiabatic
potential energy close to which simultaneous escape of electrons from a
molecule takes place are identified. The analysis of the saddles and numerical
simulations of the ionization indicate that to observe clear signatures of
simultaneous electron escape in double ionization of molecules
stronger and much shorter laser pulses than those used in the recent experiment
[E. Eremina, {\it et al}, Phys. Rev. Lett. {\bf 92}, 173001 (2004)] should be
applied.Comment: 5 pages, 3 figures, Conference proceedings from 13th International
Laser Physics Workshop, Triest, Italy, July 12-16, 200
Restricted space ab initio models for double ionization by strong laser pulses
Double electron ionisation process occurs when an intense laser pulse
interacts with atoms or molecules. Exact {\it ab initio} numerical simulation
of such a situation is extremely computer resources demanding, thus often one
is forced to apply reduced dimensionality models to get insight into the
physics of the process. The performance of several algorithms for simulating
double electron ionization by strong femtosecond laser pulses are studied. The
obtained ionization yields and the momentum distributions of the released
electrons are compared, and the effects of the model dimensionality on the
ionization dynamics discussed
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