42 research outputs found
Pseudo-time Schroedinger equation with absorbing potential for quantum scattering calculations
The Schroedinger equation with an energy-dependent complex absorbing
potential, associated with a scattering system, can be reduced for a special
choice of the energy-dependence to a harmonic inversion problem of a discrete
pseudo-time correlation function. An efficient formula for Green's function
matrix elements is also derived. Since the exact propagation up to time 2t can
be done with only t real matrix-vector products, this gives an unprecedently
efficient scheme for accurate calculations of quantum spectra for possibly very
large systems.Comment: 9 page
Coherent Control of Isotope Separation in HD+ Photodissociation by Strong Fields
The photodissociation of the HD+ molecular ion in intense short- pulsed
linearly polarized laser fields is studied using a time- dependent wave-packet
approach where molecular rotation is fully included. We show that applying a
coherent superposition of the fundamental radiation with its second harmonic
can lead to asymmetries in the fragment angular distributions, with significant
differences between the hydrogen and deuterium distributions in the long
wavelength domain where the permanent dipole is most efficient. This effect is
used to induce an appreciable isotope separation.Comment: Physical Review Letters, 1995 (in press). 4 pages in revtex format, 3
uuencoded figures. Full postcript version available at:
http://chemphys.weizmann.ac.il/~charron/prl.ps or
ftp://scipion.ppm.u-psud.fr/coherent.control/prl.p
The dynamical Green's function and an exact optical potential for electron-molecule scattering including nuclear dynamics
We derive a rigorous optical potential for electron-molecule scattering
including the effects of nuclear dynamics by extending the common many-body
Green's function approach to optical potentials beyond the fixed-nuclei limit
for molecular targets. Our formalism treats the projectile electron and the
nuclear motion of the target molecule on the same footing whereby the dynamical
optical potential rigorously accounts for the complex many-body nature of the
scattering target. One central result of the present work is that the common
fixed-nuclei optical potential is a valid adiabatic approximation to the
dynamical optical potential even when projectile and nuclear motion are
(nonadiabatically) coupled as long as the scattering energy is well below the
electronic excitation thresholds of the target. For extremely low projectile
velocities, however, when the cross sections are most sensitive to the
scattering potential, we expect the influences of the nuclear dynamics on the
optical potential to become relevant. For these cases, a systematic way to
improve the adiabatic approximation to the dynamical optical potential is
presented that yields non-local operators with respect to the nuclear
coordinates.Comment: 22 pages, no figures, accepted for publ., Phys. Rev.
The role of the geometric phases in adiabatic population tracking for non-Hermitian Hamiltonians
International audienceThe definition of instantaneous eigenstate populations for a dynamical non-self-adjoint system is not obvious. The naive direct extension of the definition used for the self-adjoint case leads to inconsistencies; the resulting artifacts can induce a false inversion of population or a false adiabaticity. We show that the inconsistency can be avoided by introducing geometric phases in another possible definition of populations. An example is given which demonstrates both the anomalous effects and their removal by our approach
Discussion of the adiabatic hypothesis in control schemes using exceptional points
International audienceWe present calculations for the action of laser pulses on vibrational transfer within the H-2(+) and Na-2 molecules in the presence of dissipation due to photodissociation of the molecule. The laser fields perform closed loops surrounding exceptional points in the laser parameter plane of intensity and wavelength. In principle the process should produce controlled vibrational transfers due to an adiabatic flip of the dressed eigenstates. We directly solve the Schrodinger equation with the complete time-dependent field instead of using the adiabatic Floquet formalism which initially suggested the design of the laser pulses. Results given by wavepacket propagations disagree with predictions obtained using the adiabatic hypothesis. Thus we show that there are large non-adiabatic exchanges and that the dissipative character of the dynamics renders the adiabatic flip very difficult to obtain. Using much longer durations than expected from previous studies, the adiabatic flip is only obtained for the Na-2 molecule and with strong dissociation