Polariton-polariton Interactions Research Articles

Suppression of Zeeman splitting and polarization steps in localized exciton-polariton condensates

We show that the condensation of exciton-polaritons in semiconductor microcavities in an applied magnetic field manifests itself in the quenching of the Zeeman splitting of an elliptically polarized condensate. The circular polarization degree of a localized condensate with a finite number of particles increases as a function of the magnetic field with a step-like behavior. The width of each polarization step is fixed by the polariton-polariton interaction constants and the number of steps is fixed by the number of polaritons in the condensate. The magnetic susceptibility of the condensate depends qualitatively on the parity of the number of polaritons.

Microscopic theory of nonlinear polariton interactions in strongly coupled hybrid organic-inorganic microcavities

We study hybrid organic-inorganic microcavities in the strong coupling regime. The optically resonant materials are an organic monolayer and a semiconductor quantum well, which are spatially separated and coupled only via the cavity photons. The hybrid cavity eigenmodes are hybrid Frenkel--Wannier-Mott exciton polaritons. We derive the nonlinear hybrid polariton-polariton interactions, which stem from the Frenkel and Wannier-Mott exciton-exciton interactions in the organic and inorganic materials, respectively. We show that such a hybrid interaction strength can be controlled by changing the exciton and cavity photon detuning energies. The linear and nonlinear response functions of a hybrid microcavity for an external field are obtained with resonances at the hybrid polariton frequencies.

Polarization Multistability of Cavity Polaritons

New effects of polarization multistability and polarization hysteresis in a coherently driven polariton system in a semiconductor microcavity are predicted and theoretically analyzed. The multistability arises due to polarization-dependent polariton-polariton interactions and can be revealed in polarization resolved photoluminescence experiments. The pumping power required to observe this effect is 4 orders of magnitude lower than the characteristic pumping power in conventional bistable optical systems.

Excitation of vortices in semiconductor microcavities

We predict that the transverse electric-magnetic polarization splitting of exciton polaritons allows a simple technique for the generation of polariton vortices of winding number 2 in semiconductor microcavities. The vortices can be excited by circularly polarized light having no orbital angular momentum and observed as phase vortices in the opposite circular polarization or directly as linear polarization vortices. The prediction is explained by a simplified analytical linear model and shown fully with a numerical model based on the Gross-Pitaevskii equations, which includes the nonlinear effects of polariton-polariton interactions.

Nonlinear effects in spin relaxation of cavity polaritons

We present the general kinetic formalism for the description of spin and energy relaxation of the cavity polaritons in the framework of the Born-Markov approximation. All essential mechanisms of polaritons redistribution in reciprocal space together with final state bosonic stimulation are taken into account, from our point of view. The developed theory is applied to describe our experimental results on the polarization dynamics obtained in the polariton parametric amplifier geometry (pumping at so-called magic angle). We have experimentally confirmed that the anisotropy of the polariton-polariton interaction is responsible for the build up of the cross-linear polarisation of the signal. The long-living linear polarization is observed at zero detuning. Under elliptical pumping, we have directly measured in the time domain and modelled the effect of self-induced Larmor precession.

Dominant Effect of Polariton-Polariton Interactions on the Coherence of the Microcavity Optical Parametric Oscillator

The importance of interaction effects in determining the temporal coherence of spectrally and spatially isolated single modes of the microcavity optical parametric oscillator (OPO) is demonstrated. As a function of macroscopic occupancy, the coherence time (tau c) first increases linearly and then exhibits saturation behavior, reaching maximum values of up to 500 ps. Good agreement is found with a model including fluctuations in polariton number and polariton-polariton interactions between the OPO states. tau c is a property of the coupled OPO system, a result confirmed by the finding of equal coherence times for signal and idler, even though the idler is subject to strong additional scattering.

Polariton parametric amplifications in organic microcavities

Nonlinear processes involving polaritons in organic crystalline microcavities are theoretically studied by taking the kinematic polariton-polariton interactions as a source of nonlinearity. The polariton mean-field equations of motion are derived and used to explain the polariton parametric amplifications, which are predicted here for angle-resolved resonant pump-probe experiments in organic microcavities. We show that around zero exciton-photon detuning and for long-wavelength polaritons in a laterally confined microcavity, the polariton kinematic interactions result in a blueshift in the amplified probe field, while for large negative detuning the amplified probe field is redshifted. The parametric amplifications are studied for different processes which include the upper and lower polariton branches.

Spatial structure and stability of the macroscopically occupied polariton state in the microcavity optical parametric oscillator

Transverse spatial images of the signal generated in semiconductor microcavities under conditions of resonant parametric scattering are obtained. When the system is pumped significantly above the threshold, the signal image is found to be highly structured, consisting of a set of localized bright spots. By comparison with a numerical model, it is shown that the structure arises from the blueshift generated by the nonlinear polariton-polariton interaction which drives the microcavity optical parametric oscillator, in combination with partially ordered spatial fluctuations in the cavity mode energy. An important outcome is that the form and stability of the signal is strongly influenced by the local cavity disorder.

Polariton quantum blockade in a photonic dot

We investigate the quantum nonlinear dynamics of a resonantly excited photonic quantum dot embedding a quantum well in the strong exciton-photon coupling regime. Within a master equation approach, we study the polariton quantum blockade and the generation of single photon states due to polariton-polariton interactions as a function of the photonic dot geometry, spectral linewidths and energy detuning between quantum well exciton and confined photon mode. The second order coherence function $g^{(2)}(t,t')$ is calculated for both continuous wave and pulsed excitations.

Effects of Bose-Einstein condensation of exciton polaritons in microcavities on the polarization of emitted light

It is shown theoretically that Bose condensation of spin-degenerated exciton-polaritons results in spontaneous buildup of the linear polarization in emission spectra of semiconductor microcavities. The linear polarization degree is a good order parameter for the polariton Bose condensation. If spin-degeneracy is lifted, an elliptically polarized light is emitted by the polariton condensate. The main axis of the ellipse rotates in time due to self-induced Larmor precession of the polariton condensate pseudospin. The polarization decay time is governed by the dephasing induced by the polariton-polariton interaction and strongly depends on the statistics of the condensed state.

Exciton-polariton kinematic interactions in organic microcavities

We analyze the exciton-exciton and polariton-polariton kinematic interactions in crystalline organic microcavities. The kinematic interactions are derived using the Agranovich-Toshich transformation, which transforms the Frenkel excitons from paulions into bosons. From the calculated exciton-scattering cross section in an organic crystalline monolayer, we find that the scattering due to the exciton-exciton kinematic interaction can be described as the scattering between hard disks. We show that, as in the case of two-dimensional ultracold trapped boson atom gas, excitons in a confined monolayer may behave as a dilute degenerate boson gas at low temperature. In an organic cavity, with an organic crystalline monolayer as a resonant material, we derive the polariton-polariton kinematic interaction, which stems from the polariton excitonic part. We calculate the polariton-scattering cross section due to the polariton-polariton kinematic interaction, and recognize the scattering effective potential. We show that, due to the smallness of the polariton effective mass, polaritons in organic cavities may behave as a dilute degenerate boson gas up to room temperature. The comparison between the polariton-polariton kinematic interaction in organic cavities and the polariton-polariton nonlinear interaction in inorganic semiconductor cavities shows that both interactions are of the same order.

Kinetics of the polariton condensate formation in a microcavity

The second-order coherence formation in the condensate of polaritons in a semiconductor microcavity is studied. The finite lifetime of polaritons allows to neglect the polariton-polariton interaction at low occupations of the polariton condensate, and the initial stage of condensate formation can be analyzed analytically. Then I discuss the decisive role of polariton-polariton repulsion and other nonlinearities in the suppression of the amplitude fluctuation of the order parameter and the second-order coherence build-up. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical bistability in semiconductor microcavities

We report the observation of polaritonic bistability in semiconductor microcavities in the strong-coupling regime. The origin of bistability is the polariton-polariton interaction, which gives rise to a Kerr-like nonlinearity. The experimental results are in good agreement with a simple model taking transverse effects into account.

Suppressed Polariton Scattering in Semiconductor Microcavities

Ultrafast time-resolved measurements on a semiconductor microcavity distinguish polariton dynamics dependent on the detuning between the constituent photon and exciton modes. Spectral synthesis allows the injection of specific polariton pulses into the sample. Scattering which results in absorption is found to be suppressed in the lower polariton branch by the combined action of normal mode splitting and motional narrowing. The experimental difference between angle and position tuning demonstrates the role of the polariton dispersion in polariton-polariton interactions.

Polarization dependence of excitonic-polariton propagation in a GaAs quantum-well waveguide.

Anisotropic propagation of excitonic polaritons in GaAs single-quantum-well waveguide structures is evidenced by means of time-of-flight measurements. This anisotropy suggests that the depolarization effect of two-dimensional excitons enhances the polariton propagation. The observed optical nonlinearity of the group velocity supports the existence of polaritons and reflects the effect of a polariton-polariton interaction on their propagation.