32 research outputs found
Quantum entanglement in strong-field ionization
We investigate the time-evolution of quantum entanglement between an
electron, liberated by a strong few-cycle laser pulse, and its parent ion-core.
Since the standard procedure is numerically prohibitive in this case, we
propose a novel way to quantify the quantum correlation in such a system: we
use the reduced density matrices of the directional subspaces along the
polarization of the laser pulse and along the transverse directions as building
blocks for an approximate entanglement entropy. We present our results, based
on accurate numerical simulations, in terms of several of these entropies, for
selected values of the peak electric field strength and the carrier-envelope
phase difference of the laser pulse. The time evolution of the mutual entropy
of the electron and the ion-core motion along the direction of the laser
polarization is similar to our earlier results based on a simple
one-dimensional model. However, taking into account also the dynamics
perpendicular to the laser polarization reveals a surprisingly different
entanglement dynamics above the laser intensity range corresponding to pure
tunneling: the quantum entanglement decreases with time in the over-the-barrier
ionization regime
Density-based one-dimensional model potentials for strong-field simulations in , and
We present results on the accurate one-dimensional (1D) modeling of simple
atomic and molecular systems excited by strong laser fields. We use atomic
model potentials that we derive from the corrections proposed earlier using the
reduced ground state density of a three-dimensional (3D) single-active electron
atom. The correction involves a change of the asymptotics of the 1D Coulomb
model potentials while maintaining the correct ground state energy. We present
three different applications of this method: we construct correct 1D models of
the hydrogen molecular ion, the helium atom and the hydrogen molecule using
improved parameters of existing soft-core Coulomb potential forms. We test
these 1D models by comparing the corresponding numerical simulation results
with their 3D counterparts in typical strong-field physics scenarios with near-
and mid-infrared laser pulses, having peak intensities in the
range, and we find an impressively increased
accuracy in the dynamics of the most important atomic quantities on the time
scale of the excitation. We also present the high-order harmonic spectra of the
He atom, computed using our 1D atomic model potentials. They show a very good
match with the structure and phase obtained from the 3D simulations in an
experimentally important range of excitation amplitudes
Quantum rings with time dependent spin-orbit coupling: Rabi oscillations, spintronic Schrodinger-cat states, and conductance properties
The strength of the (Rashba-type) spin-orbit coupling in mesoscopic
semiconductor rings can be tuned with external gate voltages. Here we consider
the case of a periodically changing spin-orbit interaction strength as induced
by sinusoidal voltages. In a closed one dimensional quantum ring with weak
spin-orbit coupling, Rabi oscillations are shown to appear. We find that the
time evolution of initially localized wave packets exhibits a series of
collapse and revival phenomena. Partial revivals -- that are typical in
nonlinear systems -- are shown to correspond to superpositions of states
localized at different spatial positions along the ring. These "spintronic
Schrodinger-cat sates" appear periodically, and similarly to their counterparts
in other physical systems, they are found to be sensitive to environment
induced disturbances. The time dependent spin transport problem, when leads are
attached to the ring, is also solved. We show that the "sideband currents"
induced by the oscillating spin-orbit interaction strength can become the
dominant output channel, even in the presence of moderate thermal fluctuations
and random scattering events.Comment: 11 pages, 9 figures, submitted to PR
Oscillations in Quantum Entanglement During Rescattering
We study the time evolution of quantum entanglement between an electron and
its parent ion during the rescattering due to a strong few-cycle laser pulse.
Based on a simple one-dimensional model, we compute the Neumann entropy during
the process for several values of the carrier-envelope phase. The local maxima
of the oscillations in the Neumann entropy coincide with the zero crossings of
the electric field of the laser pulse. We employ the Wigner function to
qualitatively explain the quantum dynamics of rescattering in the phase space.Comment: 2 page
Spintronic single qubit gate based on a quantum ring with spin-orbit interaction
In a quantum ring connected with two external leads the spin properties of an
incoming electron are modified by the spin-orbit interaction resulting in a
transformation of the qubit state carried by the spin. The ring acts as a one
qubit spintronic quantum gate whose properties can be varied by tuning the
Rashba parameter of the spin-orbit interaction, by changing the relative
position of the junctions, as well as by the size of the ring. We show that a
large class of unitary transformations can be attained with already one ring --
or a few rings in series -- including the important cases of the Z, X, and
Hadamard gates. By choosing appropriate parameters the spin transformations can
be made unitary, which corresponds to lossless gates.Comment: 4 pages, 4 figure