1,165 research outputs found
Electronic correlations in double ionization of atoms in pump-probe experiments
The ionization dynamics of a two-electron atom in an attosecond XUV-infrared
pump-probe experiment is simulated by solving the time-dependent two-electron
Schr\"odinger equation. A dramatic change of the double ionization (DI) yield
with variation of the pump-probe delay is reported and the governing role of
electron-electron correlations is shown. The results allow for a direct control
of the DI yield and of the relative strength of double and single ionization
Towards a theory of attosecond transient recorder
Laser assisted photoemission by a chirped subfemtosecond extreme ultraviolet
(XUV) pulse is considered within an exactly solvable quantum-mechanical model.
Special emphasis is given to the energy dependence of photoexcitation
cross-section. The streaked spectra are analyzed within the classical picture
of initial time-momentum distribution r_ini(p,t) of photoelectrons mapped to
the final energy scale. The actual time-momentum distribution in the absence of
the probe laser field is shown to be a poor choice for r_ini, and a more
adequate ansatz is suggested. The semiclassical theory offers a simple
practically useful approximation for streaked spectra. Its limitations for
sufficiently long chirped XUV pulses are established.Comment: 9 pages 8 figure
Anticorrelation between temperature and fluctuations in moderately damped Josephson junctions
We study the influence of dissipation on the switching current statistics of
moderately damped Josephson junctions. Different types of both low- and high-
junctions with controlled damping are studied. The damping parameter of
the junctions is tuned in a wide range by changing temperature, magnetic field,
gate voltage, introducing a ferromagnetic layer or in-situ capacitive shunting.
A paradoxical collapse of switching current fluctuations occurs with increasing
in all studied junctions. The phenomenon critically depends on dissipation
in the junction and is explained by interplay of two counteracting consequences
of thermal fluctuations, which on the one hand assist in premature switching
into the resistive state and on the other hand help in retrapping back to the
superconducting state. This is one of the rare examples of anticorrelation
between temperature and fluctuation amplitude of a physically measurable
quantity.Comment: 17 pages, 20 figure
Efficient grid-based method in nonequilibrium Green's function calculations. Application to model atoms and molecules
We propose and apply the finite-element discrete variable representation to
express the nonequilibrium Green's function for strongly inhomogeneous quantum
systems. This method is highly favorable against a general basis approach with
regard to numerical complexity, memory resources, and computation time. Its
flexibility also allows for an accurate representation of spatially extended
hamiltonians, and thus opens the way towards a direct solution of the two-time
Schwinger/Keldysh/Kadanoff-Baym equations on spatial grids, including e.g. the
description of highly excited states in atoms. As first benchmarks, we compute
and characterize, in Hartree-Fock and second Born approximation, the ground
states of the He atom, the H molecule and the LiH molecule in one spatial
dimension. Thereby, the ground-state/binding energies, densities and
bond-lengths are compared with the direct solution of the time-dependent
Schr\"odinger equation.Comment: 11 pages, 5 figures, submitted to Physical Review
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