98 research outputs found
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
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
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
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
Resonant state expansion applied to planar open optical systems
The resonant state expansion (RSE), a novel perturbation theory of
Brillouin-Wigner type developed in electrodynamics [Muljarov, Langbein, and
Zimmermann, Europhys. Lett., 92, 50010(2010)], is applied to planar,
effectively one-dimensional optical systems, such as layered dielectric slabs
and Bragg reflector microcavities. It is demonstrated that the RSE converges
with a power law in the basis size. Algorithms for error estimation and their
reduction by extrapolation are presented and evaluated. Complex
eigenfrequencies, electro-magnetic fields, and the Green's function of a
selection of optical systems are calculated, as well as the observable
transmission spectra. In particular we find that for a Bragg-mirror
microcavity, which has sharp resonances in the spectrum, the transmission
calculated using the resonant state expansion reproduces the result of the
transfer/scattering matrix method
Resonant-state expansion of dispersive open optical systems: Creating gold from sand
A resonant-state expansion (RSE) for open optical systems with a general frequency dispersion of the permittivity is presented. The RSE of dispersive systems converts Maxwell's wave equation into a linear matrix eigenvalue problem in the basis of unperturbed resonant states, in this way numerically exactly determining all relevant eigenmodes of the optical system. The dispersive RSE is verified by application to the analytically solvable system of a sphere in vacuum, with a dispersion of the permittivity described by the Drude and Drude-Lorentz models. We calculate the optical modes converting the sphere material from gold to nondispersive sand and back to gold, and evaluate the accuracy using exact solutions
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