1,172 research outputs found
Optimizing the Drude-Lorentz model for material permittivity: Examples for semiconductors
Approximating the frequency dispersion of the permittivity of materials with
simple analytical functions is of fundamental importance for understanding and
modeling their optical properties. Quite generally, the permittivity can be
treated in the complex frequency plane as an analytic function having a
countable number of simple poles which determine the dispersion of the
permittivity, with the pole weights corresponding to generalized conductivities
of the medium at these resonances. The resulting Drude-Lorentz model separates
the poles at frequencies with zero real part (Ohm's law and Drude poles) from
poles with finite real part (Lorentz poles). To find the parameters of such an
analytic function, we minimize the error weighted deviation between the model
and measured values of the permittivity. We show examples of such optimizations
for various semiconductors (Si, GaAs and Ge), for different frequency ranges
and up to five pairs of Lorentz poles accounted for in the model.Comment: arXiv admin note: substantial text overlap with arXiv:1612.0692
Quantum complementarity of microcavity polaritons
We present an experiment that probes polariton quantum correlations by
exploiting quantum complementarity. Specifically, we find that polaritons in
two distinct idler-modes interfere if and only if they share the same
signal-mode so that "which-way" information cannot be gathered. The
experimental results prove the existence of polariton pair correlations that
store the "which-way" information. This interpretation is confirmed by a
theoretical analysis of the measured interference visibility in terms of
quantum Langevin equations
Robustness of energy landscape control for spin networks under decoherence
Quantum spin networks form a generic system to describe a range of quantum
devices for quantum information processing and sensing applications.
Understanding how to control them is essential to achieve devices with
practical functionalities. Energy landscape shaping is a novel control paradigm
to achieve selective transfer of excitations in a spin network with
surprisingly strong robustness towards uncertainties in the Hamiltonians. Here
we study the effect of decoherence, specifically generic pure dephasing, on the
robustness of these controllers. Results indicate that while the effectiveness
of the controllers is reduced by decoherence, certain controllers remain
sufficiently effective, indicating potential to find highly effective
controllers without exact knowledge of the decoherence processes.Comment: 6 pages, 6 figure
Robustness of Energy Landscape Controllers for Spin Rings under Coherent Excitation Transport
The design and analysis of controllers to regulate excitation transport in
quantum spin rings presents challenges in the application of classical feedback
control techniques to synthesize effective control, and generates results in
contradiction to the expectations of classical control theory. In this paper,
we examine the robustness of controllers designed to optimize the fidelity of
an excitation transfer to uncertainty in system and control parameters. We use
the logarithmic sensitivity of the fidelity error as the measure of robustness,
drawing on the classical control analog of the sensitivity of the tracking
error. In our analysis we demonstrate that quantum systems optimized for
coherent transport demonstrate significantly different correlation between
error and the log-sensitivity depending on whether the controller is optimized
for readout at an exact time T or over a time-window about T.Comment: 10 pages, 4 figures, 2 table
Binding energy and dephasing of biexcitons in In0.18Ga0.82As/GaAs single quantum wells
Biexciton binding energies and biexciton dephasing in In0.18Ga0.82As/GaAs single quantum wells have been measured by time-integrated and spectrally resolved four-wave mixing. The biexciton binding energy increases from 1.5 to 2.6 meV for well widths increasing from 1 to 4 nm. The ratio between exciton and biexciton binding energy changes from 0.23 to 0.3 with increasing inhomogeneous broadening, corresponding to increasing well width. From the temperature dependence of the exciton and biexciton four-wave mixing signal decay, we have deduced the acoustic-phonon scattering of the exciton-biexciton transition. It is found to be comparable to that of the exciton transition, indicating that the deformation potential interactions for the exciton and the exciton-biexciton transitions are comparable
Resonant-state expansion applied to three-dimensional open optical systems: Complete set of static modes
We present two alternative complete sets of static modes of a homogeneous dielectric sphere, for their use in the resonant-state expansion (RSE), a rigorous perturbative method in electrodynamics. Physically, these modes are needed to correctly describe the static electric field of a charge redistribution within the optical system due to a perturbation of the permittivity. We demonstrate the convergence of the RSE toward the exact result for a perturbation describing a size reduction of the basis sphere. We then revisit the quarter-sphere perturbation treated by Doost et al. [Phys. Rev. A 90, 013834 (2014)], where only a single static mode for each angular momentum was introduced, and show that using a complete set of static modes leads to a small though non-negligible correction of the RSE result, improving the agreement with finite-element simulations. As another example of applying the RSE with a complete set of static modes, we calculate the resonant states of a dielectric cylinder, also comparing the result with a finite-element simulation
Resonant-state expansion of three-dimensional open optical systems: Light scattering
A rigorous method of calculating the electromagnetic field, the scattering
matrix, and scattering cross-sections of an arbitrary finite three-dimensional
optical system described by its permittivity distribution is presented. The
method is based on the expansion of the Green's function into the resonant
states of the system. These can be calculated by any means, including the
popular finite element and finite-difference time-domain methods. However,
using the resonant-state expansion with a spherically-symmetric analytical
basis, such as that of a homogeneous sphere, allows to determine a complete set
of the resonant states of the system within a given frequency range.
Furthermore, it enables to take full advantage of the expansion of the field
outside the system into vector spherical harmonics, resulting in simple
analytic expressions. We verify and illustrate the developed approach on an
example of a dielectric sphere in vacuum, which has an exact analytic solution
known as Mie scattering
Coherence dynamics and quantum-to-classical crossover in an exciton-cavity system in the quantum strong coupling regime
Interaction between light and matter generates optical nonlinearities, which are particularly pronounced in the quantum strong coupling regime. When a single bosonic mode couples to a single fermionic mode, a Jaynes-Cummings (JC) ladder is formed, which we realize here using cavity photons and quantum dot excitons. We measure and model the coherent anharmonic response of this strongly coupled exciton-cavity system at resonance. Injecting two photons into the cavity, we demonstrate a root 2 larger polariton splitting with respect to the vacuum Rabi splitting. This is achieved using coherent nonlinear spectroscopy, specifically four-wave mixing, where the coherence between the ground state and the first (second) rung of the JC ladder can be interrogated for positive (negative) delays. With increasing excitation intensity and thus rising average number of injected photons, we observe spectral signatures of the quantum-to-classical crossover of the strong coupling regime.Peer reviewe
Retarded Casimir-Polder force on an atom near reflecting microstructures
We derive the fully retarded energy shift of a neutral atom in two different
geometries useful for modelling etched microstructures. First we calculate the
energy shift due to a reflecting cylindrical wire, and then we work out the
energy shift due to a semi-infinite reflecting half-plane. We analyze the
results for the wire in various limits of the wire radius and the distance of
the atom from the wire, and obtain simple asymptotic expressions useful for
estimates. For the half-plane we find an exact representation of the
Casimir-Polder interaction in terms of a single, fast converging integral,
which is easy to evaluate numerically.Comment: 12 pages, 8 figure
Spin recovery in the 25nm gate length InGaAs field effect transistore
We augmented an ensemble Monte-Carlo semiconductor device simulator [3] to incorporate electron spin degrees of freedom using a Bloch equation model to investigate the feasibility of spintronic devices. Results are presented for the steady state polarization and polarization decay due to scattering and spin orbit coupling for a III-V MOSFET device as a function of gate voltages, injection polarization and strain
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