N. H. Kwong

Electromagnetically induced transparency via electron spin coherence in a quantum well waveguide

We propose and analyze a novel scheme to realize electromagnetically induced transparency (EIT) via robust electron spin coherence in semiconductor quantum wells. This scheme uses light hole transitions in a quantum well waveguide to induce electron spin coherence in the absence of an external magnetic field. For certain polarization configurations, the light hole transitions form a crossed double-V system. EIT in this system is strongly modified by a coherent wave mixing process induced by the electron spin coherence.

Influence of exciton-exciton correlations on the polarization characteristics of polariton amplification in semiconductor microcavities

Based on a microscopic many-particle theory we investigate the influence of excitonic correlations on the vectorial polarization state characteristics of the parametric amplification of polaritons in semiconductor microcavities. We study a microcavity with perfect in-plane isotropy. A linear stability analysis of the cavity polariton dynamics shows that in the co-linear (TE-TE or TM-TM) pump-probe polarization state configuration, excitonic correlations diminish the parametric scattering process whereas it is enhanced by excitonic correlations in the cross-linear (TE-TM or TM-TE) configuration. Without any free parameters, our microscopic theory gives a quantitative understanding how many-particle effects can lead to a rotation or change of the outgoing (amplified) probe signals vectorial polarization state relative to the incoming ones.

Semiconductor Kadanoff-Baym Equation Results for Optically Excited Electron–Hole Plasmas in Quantum Wells

We present results from solutions of the semiconductor Kadanoff-Baym equations (full two-time semiconductor Bloch equations) with self-energies in quasistatic Born approximation, for GaAs single quantum wells. We concentrate on memory and correlation effects under fs-pulse excitation conditions. A remarkable feature is the observed kinetic energy increase which is due to the build-up of correlations among the generated carriers. We demonstrate that the two-time approach is (i) very well suited to study correlation phenomena both on short and long times, thereby avoiding well-known problems of one-time kinetic equations, and (ii) that it is becoming practical with the use of efficient integration techniques.

Inducing electron spin coherence in GaAs quantum well waveguides: spin coherence without spin precession

Electron spin coherence is induced via light-hole transitions in a quantum well waveguide without a DC magnetic field. The spin coherence is detected through effects of quantum interference in spectral domain nonlinear optical response.

Formation and control of Turing patterns in a coherent quantum fluid

A generalization of Turing patterns, originally developed for chemical reactions, to patterns in quantum fluids can be realized with microcavity polaritons. Theoretical concepts of formation and control, together with experimental observations, will be presented.

On the identification of intervalence-band coherences in semiconductor quantum wells

A theoretical analysis of intervalence-band coherences is presented. These optically created non-radiative coherences are generalizations of non-radiative coherences in atomic and molecular three-level systems. Whereas in three-level systems these coherences are the basis of important and well-established nonlinear effects, the interpretation of experimental evidence for such coherences in semiconductors needs to be supported by many-body theory. Based on the dynamics-controlled truncation formalism, the respective contributions of intervalence-band coherences and coherent biexcitonic correlations in time-integrated differential transmission spectroscopy is investigated. It is found that the contribution of the biexcitonic correlations to the observable heavy-hole–light-hole beats can be eliminated, either by reducing the light pulse duration or by choosing the central frequency of the light pulses at the heavy-hole exciton.

Transverse optical instability patterns in semiconductor microcavities: polariton scattering and low-intensity all-optical switching

(Received 26 February 2013; published 20 May 2013)We present a detailed theoretical study of transverse exciton-polariton patterns in semiconductor quantumwell microcavities. These patterns are initiated by directional instabilities (driven mainly by polariton-polaritonscattering) in the uniform pump-generated polariton field and are measured as optical patterns in a transverseplane in the far field. Based on a microscopic many-particle theory, we investigate the spatiotemporal dynamicsoftheformation,selection,andopticalcontrolofthesepatterns.Anemphasisisplacedonapreviouslyproposedlow-intensity, all-optical switching scheme designed to exploit these instability-driven patterns. Simulations anddetailed analyses of simplified and more physically transparent models are used. Two aspects of the problemare studied in detail. First, we study the dependencies of the stability behaviors of various patterns, as well astransition time scales, on parameters relevant to the switching action. These parameters are the degree of built-inazimuthal anisotropy in the system and the switching (control) beam intensity. It is found that if the parametersare varied incrementally, the pattern system undergoes abrupt transitions at threshold parameter values, whichare accompanied by multiple-stability and hysteresis behaviors. Moreover, during a real-time switching action,the transient dynamics of the system, in particular, the transition time scale, may depend significantly on theproximity of unstable patterns. The second aspect is a classification and detailed analysis of the polaritonscatteringprocessescontributingtothepatterndynamics,givingusanunderstandingoftheselectionandcontrolof patterns as results of these processes’ intricate interplay. The crucial role played by the (relative) phases of thepolariton amplitudes in determining the gains and/or losses of polariton densities in various momentum modesis highlighted. As a result of this analysis, an interpretation of the actions of the various processes in terms ofconcepts commonly used in classical pattern-forming systems is given.DOI: 10.1103/PhysRevB.87.205307 PACS number(s): 71

Large optical gain from four-wave mixing instabilities in semiconductor quantum wells

Based on a microscopic many-particle theory, we predict large optical gain in the probe and background-free four-wave mixing directions caused by excitonic instabilities in semiconductor quantum wells. For a single quantum well with radiative-decay limited dephasing in a typical pump-probe setup we discuss the microscopic driving mechanisms and polarization and frequency dependence of these instabilities.

Controlling the optical spin Hall effect with light

The optical spin Hall effect is a transport phenomenon of exciton polaritons in semiconductor microcavities, caused by the polaritonic spin-orbit interaction, which leads to the formation of spin textures. The control of the optical spin Hall effect via light injection in a double microcavity is demonstrated. Angular rotations of the polarization pattern up to 22° are observed and compared to a simple theoretical model. The device geometry is responsible for the existence of two polariton branches which allows a robust independent control of the polariton spin and hence the polarization state of the emitted light field, a solution technologically relevant for future spin-optronic devices.

Effect of n-p-n heterostructures on interface recombination and semiconductor laser cooling

The design of doped n-p-n semiconductor heterostructures has a significant influence on the structures’ nonradiative decay and can also affect their photoluminescence characteristics. Such structures have recently been explored in the context of semiconductor laser cooling. We present a theoretical analysis of optically excited n-p-n structures, focusing mainly on the influence of the layer thicknesses and doping concentrations on nonradiative interface recombination. We find that high levels of n-doping (1019 cm−3) can reduce the minority-carrier density at the interface and increase the nonradiative lifetime. We calculate time-dependent luminescence decay and find them to be in good agreement with experiment for temperatures >120 K, which is the temperature range in which our model assumptions are expected to be valid. A theoretical analysis of the cooling characteristics of n-p-n structures elucidates the interplay of nonradiative, radiative, and Auger recombination processes. We show that at high opti...