P. Lewandowski

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.

All-optical flow control of a polariton condensate using nonresonant excitation

The Dortmund group acknowledges support from the Deutsche Forschungsgemeinschaft (Grants 1549/18-1 and SFB TRR 142). The Paderborn group is grateful for financial support from the Deutsche Forschungsgemeinschaft (GRK 1464, SFB TRR 142, and SCHU 1980/5-1) and acknowledges a grant for computing time from the PC2 Paderborn Center for Parallel Computing. The group at Wurzburg University acknowledges support from the State of Bavaria. S. H. acknowledges support by the Royal Society and the Wolfson Foundation.

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

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.

Experimental realization of a polariton beam amplifier

In this report we demonstrate a novel concept for a planar cavity polariton beam amplifier using non-resonant excitation. In contrast to resonant excitation schemes, background carriers are injected which form excitons, providing both gain and a repulsive potential for a polariton condensate. Using an attractive potential environment induced by a locally elongated cavity layer, the repulsive potential of the injected background carriers is compensated and a significant amplification of polariton beams is achieved without beam distortion.

Polarization dependence of nonlinear wave mixing of spinor polaritons in semiconductor microcavities

The pseudo-spin dynamics of propagating exciton-polaritons in semiconductor microcavities are known to be strongly influenced by TE-TM splitting. As a vivid consequence, in the Rayleigh scattering regime, the TE-TM splitting gives rise to the optical spin Hall effect (OSHE). Much less is known about its role in the nonlinear optical regime in which four-wave mixing for example allows the formation of spatial patterns in the polariton density, such that hexagons and two-spot patterns are observable in the far field. Here we present a detailed analysis of spin-dependent four-wave mixing processes, by combining the (linear) physics of TE-TM splitting with spin-dependent nonlinear processes, i.e., exciton-exciton interaction and fermionic phase-space filling. Our combined theoretical and experimental study elucidates the complex physics of the four-wave mixing processes that govern polarization and orientation of off-axis modes.

Patterns and switching dynamics in polaritonic quantum fluids in semiconductor microcavities [Invited]

The occurrence of instability-driven polariton density patterns in semiconductor quantum-well microcavities has been predicted and demonstrated experimentally. Simulations have shown that different patterns can become dominant under variations of excitation and structural conditions. We have devised and analyzed low-dimensional models to help understand the physics underlying these patterns’ competition. This paper reviews the results of these model studies, mainly on optical switching of the patterns. We also present results on how the control beam strength required for switching and the time scale of switching vary with physical parameters.

Theory of optically controlled anisotropic polariton transport in semiconductor double microcavities

Exciton polaritons in semiconductor microcavities exhibit many fundamental physical effects, with some of them amenable to being controlled by external fields. The polariton transport is affected by the polaritonic spin–orbit interaction, which is caused by the splitting of transverse-electric and transverse-magnetic modes. This is the basis for a polaritonic Hall effect, called the optical spin Hall effect (OSHE), which is related to the formation of spin/polarization textures in momentum space, determining anisotropic ballistic transport, as well as related textures in real space. Owing to Coulombic interactions between the excitonic components of the polaritons, optical excitation of polaritons can affect the OSHE. We present a theoretical analysis of the OSHE and its optical control in semiconductor double microcavities, i.e., two optically coupled cavities, which are particularly well suited for the creation of polaritonic reservoirs that affect the spin-texture-forming polaritons. The theory is formulated in terms of a set of double-cavity spinor-polariton Gross–Pitaevskii equations. Numerical solutions feature, among other things, a controlled rotation of the spin texture in momentum space. The theory also allows for an identification of the effective magnetic field component that determines the optical control in phenomenological pseudo-spin models in terms of exciton interactions and the polariton density in the second lower polariton branch.

Polariton formalism for semiconductor double microcavities

In this paper, we present a polariton description of a semiconductor double microcavity system. The polariton formalism is derived from a microscopic theory for the exciton fields inside the quantum wells coupled to the confined optical cavity fields in a double cavity system. The polariton picture helps simplify theoretical studies of the observed phenomena in the double cavity system, such as nonlinear optical spin Hall effect.

Optical control of polaritons: from optoelectronic to spinoptronic device concepts

Exciton-polaritons in semiconductor microcavities have been studied intensely, both with respect to their intriguing fundamental physical properties and with respect to their potential in novel device designs. The latter requires ways to control polaritonic systems, and all-optical control mechanisms are considered to be especially useful. In this talk, we discuss and review our efforts to control the polariton density, utilizing optical four-wave mixing instabilites, and the spin or polarization textures resulting from the optical spin Hall effect. Both effects are readily observable in the cavity’s far-field emission, and hence potentially useful for optoelectronic and spinoptronic device applications.