329 research outputs found
Stimulated Raman adiabatic passage into continuum
We propose a technique which produces nearly complete ionization of the
population of a discrete state coupled to a continuum by a two-photon
transition via a lossy intermediate state whose lifetime is much shorter than
the interaction duration. We show that using counterintuitively ordered pulses,
as in stimulated Raman adiabatic passage (STIRAP), wherein the pulse coupling
the intermediate state to the continuum precedes and partly overlaps the pulse
coupling the initial and intermediate states, greatly increases the ionization
signal and strongly reduces the population loss due to spontaneous emission
through the lossy state. For strong spontaneous emission from that state,
however, the ionization is never complete because the dark state required for
STIRAP does not exist. We demonstrate that this drawback can be eliminated
almost completely by creating a laser-induced continuum structure (LICS) by
embedding a third discrete state into the continuum with a third control laser.
This LICS introduces some coherence into the continuum, which enables a
STIRAP-like population transfer into the continuum. A highly accurate analytic
description is developed and numerical results are presented for Gaussian pulse
shapes
An achromatic polarization retarder realized with slowly varying linear and circular birefringence
Using the phenomena of linear and circular birefringence we propose a device
that can alter general elliptical polarization of a beam by a predetermined
amount, thereby allowing conversion between linearly-polarized light and
circularly polarized light or changes to the handedness of the polarization.
Based on an analogy with two-state adiabatic following of quantum optics, the
proposed device is insensitive to the frequency of the light -- it serves as an
achromatic polarization retarder
Stimulated Raman Adiabatic Passage (STIRAP) Among Degenerate-Level Manifolds
We examine the conditions needed to accomplish stimulated Raman adiabatic
passage (STIRAP) when the three levels (g, e and f) are degenerate, with
arbitrary couplings contributing to the pump-pulse interaction (g - e) and to
the Stokes-pulse interaction (e-f). We show that in general a sufficient
condition for complete population removal from the g set of degenerate states
for arbitrary, pure or mixed, initial state is that the degeneracies should not
decrease along the sequence g, e and f. We show that when this condition holds
it is possible to achieve the degenerate counterpart of conventional STIRAP,
whereby adiabatic passage produces complete population transfer. Indeed, the
system is equivalent to a set of independent three-state systems, in each of
which a STIRAP procedure can be implemented. We describe a scheme of unitary
transformations that produces this result. We also examine the cases when this
degeneracy constraint does not hold, and show what can be accomplished in those
cases. For example, for angular momentum states when the degeneracy of the g
and f levels is less than that of the e level we show how a special choice for
the pulse polarizations and phases can produce complete removal of population
from the g set. Our scheme can be a powerful tool for coherent control in
degenerate systems, because of its robustness when selective addressing of the
states is not required or impossible. We illustrate the analysis with several
analytically solvable examples, in which the degeneracies originate from
angular momentum orientation, as expressed by magnetic sublevels.Comment: 21 pages, 17 figure
Spin-1/2 sub-dynamics nested in the quantum dynamics of two coupled qutrits
In this paper we investigate the quantum dynamics of two spin-1 systems,
and , adopting a generalized
-nonconserving Heisenberg model. We
show that, due to its symmetry property, the nine-dimensional dynamics of the
two qutrits exactly decouples into the direct sum of two sub-dynamics living in
two orthogonal four- and five-dimensional subspaces. Such a reduction is
further strengthened by our central result consisting in the fact that in the
four-dimensional dynamically invariant subspace, the two qutrits quantum
dynamics, with no approximations, is equivalent to that of two non interacting
spin 1/2's. The interpretative advantages stemming from such a remarkable and
non-intuitive nesting are systematically exploited and various intriguing
features consequently emerging in the dynamics of the two qutrits are deeply
scrutinised. The possibility of exploiting the dynamical reduction brought to
light in this paper for exactly treating as well time-dependent versions of our
Hamiltonian model is briefly discussed.Comment: 14 pages, 11 figures; Last two authors name corrected, corrected
typos, Fig. 11 changed (same result
Optimum pulse shapes for stimulated Raman adiabatic passage
Stimulated Raman adiabatic passage (STIRAP), driven with pulses of optimum
shape and delay has the potential of reaching fidelities high enough to make it
suitable for fault-tolerant quantum information processing. The optimum pulse
shapes are obtained upon reduction of STIRAP to effective two-state systems. We
use the Dykhne-Davis-Pechukas (DDP) method to minimize nonadiabatic transitions
and to maximize the fidelity of STIRAP. This results in a particular relation
between the pulse shapes of the two fields driving the Raman process. The
DDP-optimized version of STIRAP maintains its robustness against variations in
the pulse intensities and durations, the single-photon detuning and possible
losses from the intermediate state.Comment: 8 pages, 6 figures. submitted to Phys. Rev.
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