254 research outputs found
Nonlinear optical response and exciton dephasing in quantum dots
The full time-dependent four-wave mixing polarization in quantum dots is
microscopically calculated, taking into account acoustic phonon-assisted
transitions between different exciton states of the dot. It is shown that quite
different dephasing times of higher exciton states in pancake anisotropic
InGaAs quantum dots are responsible for the experimentally observed [1]
double-exponential decay in the photon echo signal.Comment: NOEKS-8 contribution; 4 pages, 3 figure
Exciton dephasing in quantum dots: Coupling to LO phonons via excited states
We have found a novel mechanism of spectral broadening and dephasing in
quantum dots (QDs) due to the coupling to longitudinal-optical (LO) phonons. In
theory, this mechanism comes into play only if the complete manifold of exciton
levels (including those in the wetting-layer continuum) is taken into account.
We demonstrate this nontrivial dephasing in different types of QDs, using the
exactly solvable quadratic coupling model, here generalized to an arbitrary
number of excitonic states.Comment: OECS10 contribution pape
Resonant-state expansion for open optical systems: Generalization to magnetic, chiral, and bi-anisotropic materials
The resonant-state expansion, a recently developed powerful method in
electrodynamics, is generalized here for open optical systems containing
magnetic, chiral, or bi-anisotropic materials. It is shown that the key matrix
eigenvalue equation of the method remains the same, but the matrix elements of
the perturbation now contain variations of the permittivity, permeability, and
bi-anisotropy tensors. A general normalization of resonant states in terms of
the electric and magnetic fields is presented.Comment: 4 page
Resonant states in double and triple quantum wells
The full set of resonant states in double and triple quantum well/barrier
structures is investigated. This includes bound, anti-bound and normal resonant
states which are all eigensolutions of Schrodinger's equation with generalized
outgoing wave boundary conditions. The transformation of resonant states and
their transitions between different subgroups as well as the role of each
subgroup in observables, such as the quantum transmission, is analyzed. The
quantum well potentials are modeled by Dirac delta functions; therefore, as
part of this study, the well-known problem of bound states in delta-like
potentials is also revisited.Comment: 10 pages, 11 figure
Exciton effective mass enhancement in coupled quantum wells in electric and magnetic fields
We present a calculation of exciton states in semiconductor coupled quantum
wells (CQWs) in the presence of electric and magnetic fields applied
perpendicular to the QW plane. The exciton Schr\"odinger equation is solved in
real space in three dimensions to obtain the Landau levels of both direct and
indirect excitons. Calculation of the exciton energy levels and oscillator
strengths enables mapping of the electric and magnetic field dependence of the
exciton absorption spectrum. For the ground state of the system, we evaluate
the Bohr radius, optical lifetime, binding energy and dipole moment. The
exciton mass renormalization due to the magnetic field is calculated using a
perturbative approach. We predict a non-monotonous dependence of the exciton
ground state effective mass on magnetic field. Such a trend is explained in a
classical picture, in terms of the ground state tending from an indirect to a
direct exciton with increasing magnetic field.Comment: 20 pages, 7 figure
Phonon-Induced Dephasing in Quantum Dot-Cavity QED
We present a semi-analytic and asymptotically exact solution to the problem
of phonon-induced decoherence in a quantum dot-microcavity system. Particular
emphasis is placed on the linear polarization and optical absorption, but the
approach presented herein may be straightforwardly adapted to address any
elements of the exciton-cavity density matrix. At its core, the approach
combines Trotter's decomposition theorem with the linked cluster expansion. The
effects of the exciton-cavity and exciton-phonon couplings are taken into
account on equal footing, thereby providing access to regimes of comparable
polaron and polariton timescales. We show that the optical decoherence is
realized by real phonon-assisted transitions between different polariton states
of the quantum dot-cavity system, and that the polariton line broadening is
well-described by Fermi's golden rule in the polariton frame. We also provide
purely analytic approximations which accurately describe the system dynamics in
the limit of longer polariton timescales
Exact mode volume and Purcell factor of open optical systems
The Purcell factor quantifies the change of the radiative decay of a dipole
in an electromagnetic environment relative to free space. Designing this factor
is at the heart of photonics technology, striving to develop ever smaller or
less lossy optical resonators. The Purcell factor can be expressed using the
electromagnetic eigenmodes of the resonators, introducing the notion of a mode
volume for each mode. This approach allows to use an analytic treatment,
consisting only of sums over eigenmode resonances, a so-called spectral
representation. We show in the present work that the expressions for the mode
volumes known and used in literature are only approximately valid for modes of
high quality factor, while in general they are incorrect. We rectify this
issue, introducing the exact normalization of modes. We present an analytic
theory of the Purcell effect based on the exact mode normalization and
resulting effective mode volume. We use a homogeneous dielectric sphere in
vacuum, which is analytically solvable, to exemplify these findings.Comment: Letter: 5 pages, 2 figures. Supplementary material: 16 pages, 10
figure
Controlled strong coupling and absence of dark polaritons in microcavities with double quantum wells
We demonstrate an efficient switching between strong and weak exciton-photon
coupling regimes in microcavity-embedded asymmetric double quantum wells,
controlled by an applied electric field. We show that a fine tuning of the
electric field leads to drastic changes in the polariton properties, with the
polariton ground state being red-shifted by a few meV and having acquired
prominent features of a spatially indirect dipolar exciton. We study the
properties of dipolar exciton polaritons, called dipolaritons, on a microscopic
level and show that, unlike recent findings, they are not dark polaritons but,
owing to the finite size of the excition, are mixed states with comparable
contribution of the cavity photon, bright direct, and long-living indirect
exciton modes.Comment: 5 pages, 5 figures, and supplementary materia
Comment on "Dephasing Times in Quantum Dots due to Elastic LO Phonon-Carrier Collisions"
This paper is a Comment on Phys. Rev. Lett. 85, 1516 (2000) by A.V. Uskov,
A.-P. Jauho, B. Tromborg, J. Mork, and R. Lang.Comment: 1 page, 1 figure. Phys. Rev. Lett., accepte
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