3,588 research outputs found
Long-range Energy Transfer and Ionization in Extended Quantum Systems Driven by Ultrashort Spatially Shaped Laser Pulses
The processes of ionization and energy transfer in a quantum system composed
of two distant H atoms with an initial internuclear separation of 100 atomic
units (5.29 nm) have been studied by the numerical solution of the
time-dependent Schr\"odinger equation beyond the Born-Oppenheimer
approximation. Thereby it has been assumed that only one of the two H atoms was
excited by temporally and spatially shaped laser pulses at various laser
carrier frequencies. The quantum dynamics of the extended H-H system, which was
taken to be initially either in an unentangled or an entangled ground state,
has been explored within a linear three-dimensional model, including two z
coordinates of the electrons and the internuclear distance R. An efficient
energy transfer from the laser-excited H atom (atom A) to the other H atom
(atom B) and the ionization of the latter have been found. It has been shown
that the physical mechanisms of the energy transfer as well as of the
ionization of atom B are the Coulomb attraction of the laser driven electron of
atom A by the proton of atom B and a short-range Coulomb repulsion of the two
electrons when their wave functions strongly overlap in the domain of atom B.Comment: 11 pages, 7 figure
Numerical Integrators for Highly Oscillatory Hamiltonian Systems: A Review
Numerical methods for oscillatory, multi-scale Hamiltonian systems are reviewed. The construction principles are described, and the algorithmic and analytical distinction between problems with nearly constant high frequencies and with time- or state-dependent frequencies is emphasized. Trigonometric integrators for the first case and adiabatic integrators for the second case are discussed in more detail
Monster black holes
A combination of ground-based and spacecraft observations has uncovered two
black holes of 10 billion solar masses in the nearby Universe. The finding
sheds light on how these cosmic monsters co-evolve with galaxies.Comment: 2 pages, 1 figure, LaTeX. Published in Nature "News & Views
HE 0047-1756: A new gravitationally lensed double QSO
The quasar HE 0047-1756, at z=1.67, is found to be split into two images
1.44" apart by an intervening galaxy acting as a gravitational lens. The flux
ratio for the two components is roughly 3.5:1, depending slightly upon
wavelength. The lensing galaxy is seen on images obtained at 800 nm and 2.1
\mu; there is also a nearby faint object which may be responsible for some
shear. The spectra of the two quasar images are nearly identical, but the
emission line ratio between the two components scale differently from the
continuum. Moreover, the fainter component has a bluer continuum slope than the
brighter one. We argue that these small differences are probably due to
microlensing. There are hints of an Einstein ring emanating from the brighter
image toward the fainter one.Comment: 4 pages, submitted to A&A Letter
Mapping the ionised gas around the luminous QSO HE 1029-1401: Evidence for minor merger events?
We present VIMOS integral field spectroscopy of the brightest radio-quiet QSO
on the southern sky HE 1029-1401 at a redshift of z=0.086. Standard
decomposition techniques for broad-band imaging are extended to integral field
data in order to deblend the QSO and host emission. We perform a tentative
analysis of the stellar continuum finding a young stellar population (<100Myr)
or a featureless continuum embedded in an old stellar population (10Gyr)
typical for a massive elliptical galaxy. The stellar velocity dispersion of
sigma_*=320\pm90 km/s and the estimated black hole mass
log(M_BH/M_sun)=8.7\pm0.3 are consistent with the local M_BH-sigma_* relation
within the errors. For the first time we map the two-dimensional ionised gas
distribution and the gas velocity field around HE 1029-1401. While the stellar
host morphology is purely elliptical we find a highly structured distribution
of ionised gas out to 16 kpc from the QSO. The gas is highly ionised solely by
the QSO radiation and has a significantly lower metallicity than would be
expected for the stellar mass of the host, indicating an external origin of the
gas most likely due to minor mergers. We find a rotating gas disc around the
QSO and a dispersion-dominated non-rotating gas component within the central 3
kpc. At larger distances the velocity field is heavily disturbed, which could
be interpreted as another signature of past minor merger events. Alternatively,
the arc-like structure seen in the ionised gas might also be indicative of a
large-scale expanding bubble, centred on and possibly driven by the active
nucleus.Comment: 13 pages, 13 figures, 1 table, accepted for publication in A&
Influence of Coulomb and Phonon Interaction on the Exciton Formation Dynamics in Semiconductor Heterostructures
A microscopic theory is developed to analyze the dynamics of exciton
formation out of incoherent carriers in semiconductor heterostructures. The
carrier Coulomb and phonon interaction is included consistently. A cluster
expansion method is used to systematically truncate the hierarchy problem. By
including all correlations up to the four-point (i.e. two-particle) level, the
fundamental fermionic substructure of excitons is fully included. The analysis
shows that the exciton formation is an intricate process where Coulomb
correlations rapidly build up on a picosecond time scale while phonon dynamics
leads to true exciton formation on a slow nanosecond time scale.Comment: 18 pages, 7 figure
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