Multistability of the optical response in a system of quasi-two-dimensional exciton polaritons

The nonlinear dynamic properties of a system of polaritons in a planar semiconductor microcavity under conditions of external coherent photoexcitation have been investigated. It has been shown that the interaction between polaritons with identical projections of the total angular momentum (J _z ) can give rise to multistability of the response of the excited polariton state. As a result, nonequilibrium transitions between different stability branches become possible due to fluctuations or arbitrarily smooth variations of the excitation parameters and occur with abrupt changes in the intensity and optical polarization of the field in the microcavity. It has been demonstrated that a relatively weak attraction between polaritons with opposite total angular momenta J _z leads to a possibility of spontaneously breaking the symmetry of circularly polarized field components in the microcavity under strictly linear (symmetric) polarization conditions of external excitation.     

Motional narrowing in semiconductor microcavities

We describe experiments on a semiconductor microcavity which provide the first demonstration of motional narrowing in semiconductor inter-subband optical transitions. Significant narrowing occurs because of the small mass of the polaritons in a microcavity. The demonstration is made possible by the control provided in a microcavity of the mixing between photon and exciton states, and hence the dispersion of the polariton.     

Diamagnetism of microcavity polaritons induced by spin-dependent polariton–polariton interactions

Diamagnetism of condensed microcavity polaritons in a vertically applied magnetic field is theoretically studied by using the density of free energy of polaritons. The magnetic dependence of polariton–polariton interactions and spin polarization degree of polaritons are derived, and are used to show the diamagnetic behavior of the polariton spin polarization, which is discussed for GaAs-based microcavities. We show that for strong magnetic field the spin polarization of the polaritons is paramagnetic as usual, while around positive exciton–photon detuning and special Rabi splitting, the spin polarization of the polaritons could be diamagnetic. In addition, weak magnetic field and high polariton density are beneficial to observe the polariton diamagnetism.     

Quantum degenerate exciton-polaritons in thermal equilibrium

We study the momentum distribution and relaxation dynamics of semiconductor microcavity polaritons by angle-resolved and time-resolved spectroscopy. Above a critical pump level, the thermalization time of polaritons at positive detunings becomes shorter than their lifetime, and the polaritons form a quantum degenerate Bose-Einstein distribution in thermal equilibrium with the lattice.     

On the mechanism of the maintenance of Rabi oscillations in the system of exciton polaritons in a microcavity

A physical mechanism of the implementation of undamped Rabi oscillations in the system of exciton polaritons in a semiconductor microcavity in the presence of nonresonant pumping has been proposed. Various mechanisms of the stimulated scattering of excitons from the reservoir have been considered. It has been shown that undamped oscillations of the population of the photon component of the condensate can be caused by the feeding of a coherent Rabi oscillator owing to the pair scattering of excitons from the reservoir to the ground state. The effect should be observed in spite of a more intense relaxation of polaritons of the upper branch observed experimentally.     

Polarization selection rules in scattering of cavity polaritons

We theoretically discuss scattering of polaritons in semiconductor microcavities by means of a microscopic model. Taking into account the composite character of excitons (formed by an electron and a hole), we analyze the relation between polarizations of incoming and outgoing polariton states under resonant excitation by linearly polarized laser beams with opposite in-plane momenta. In addition to these polarization selection rules, we investigate the nonlinear processes up to the sixth order and we show the origin of an induced anisotropy due to the excitation beams which is responsible for the operation of an optical gate based on polariton–polariton scattering in a microcavity.     

GaAs量子阱半导体微腔中腔极化激元的动态行为

GaAs量子阱半导体微腔中, 光子同时与重空穴激子、轻空穴激子耦合形成腔极化激元. 本文采用三谐振子耦合模型, 计算了腔极化激元的三支的色散关系、线宽、有效质量及其群速度; 结果表明, 由于腔极化激元的三支中光子、重空穴激子、轻空穴激子所占的权重随着平面波矢（或入射角度）变化, 腔极化激元三支的线宽、有效质量及其群速度呈现出不同的动态行为.     

Thermodynamics and excitations of condensed polaritons in disordered microcavities

We study the thermodynamic condensation of microcavity polaritons using a realistic model of disorder in semiconductor quantum wells. This approach correctly describes the polariton inhomogeneous broadening in the low density limit, and treats scattering by disorder to all orders in the condensed regime. While the weak disorder changes the thermodynamic properties of the transition little, the effects of disorder in the condensed state are prominent in the excitations and can be seen in resonant Rayleigh scattering.     

Spin-dependent coexistence of weakly coupled and strongly coupled modes in semiconductor microcavities

The dependence of the transition from the strong-coupling regime to the weak-coupling regime on the polariton spin orientation in a InGaAs semiconductor microcavity is experimental studied by means of time-resolved photoluminescence. Polaritons are created by non-resonant circularly-polarized optical excitation and the power intensity that breaks the strong coupling is found to be much lower for co-polarized polaritons than that for cross-polarized polaritons. Coulomb screening effects alone cannot explain the stronger loss of oscillator strength for majority excitons (co-polarized) and spin-dependent mechanisms are required to justify such behaviour.     

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.     

Quantum degeneracy of microcavity polaritons

We investigate experimentally one of the main features of a quantum fluid constituted by exciton polaritons in a semiconductor microcavity, that is, quantum degeneracy of a macroscopic fraction of the particles. We show that resonant pumping allows us to create a macroscopic population of polaritons in one quantum state. Furthermore, we demonstrate that parametric polariton scattering results in the transfer of a macroscopic population of polariton from one single quantum state into another one. Finally, we briefly outline a simple method which provides direct evidence of the first-order spatial coherence of the transferred population.     

Spatial condensation of trapped polaritons in graphene and semiconductor structures

The theoretical and experimental status of the Bose–Einstein Condensation (BEC) of trapped quantum well (QW) polaritons in a microcavity is presented. The results of recent experiments that have shown the possibility to create an in-plane harmonic potential trap for a two-dimensional (2D) exciton polaritons in a cavity are discussed. We report the theory of BEC and of the trapped QW exciton polaritons in a microcavity. In addition, we study the BEC of trapped magnetoexciton polaritons in a graphene layer (GL) embedded in an optical microcavity in high magnetic field. In both cases the polaritons are considered to be in a harmonic potential trap. We compare the theoretical results with the existing experiments and discuss the experimental observation of predicted phenomena.     

Excitations in a nonequilibrium Bose-Einstein condensate of exciton polaritons

We develop a mean-field theory of the dynamics of a nonequilibrium Bose-Einstein condensate of exciton polaritons in a semiconductor microcavity. The spectrum of elementary excitations around the stationary state is analytically studied by means of a generalized Gross-Pitaevskii equation. A diffusive behavior of the Goldstone mode is found in the spatially homogeneous case and new features are predicted for the Josephson effect in a two-well geometry.     

Modification of the photoluminescence anisotropy of semiconductor nanowires by coupling to surface plasmon polaritons

We demonstrate efficient modification of the polarized light emission from single semiconductor nanowires by coupling this emission to surface plasmon polaritons on a metal grating. The polarization anisotropy of the emitted photoluminescence from single nanowires is compared for wires deposited on silica, a flat gold film, and a shallow gold grating. By varying the orientation of the nanowire with respect to the grating grooves, the large intrinsic polarization anisotropy can be either suppressed or enhanced. This modification is interpreted by the appearance of an additional emission channel induced by surface plasmon polaritons and their conversion to p-polarized radiation at the grating.     

半导体微腔中腔模、重空穴激子模和轻空穴激子模耦合

采用传输矩阵方法利用半经典的线性色散模型,计算半导体微腔内同时存在重空穴激子、轻空穴激子时,在不同入射角度下的反射谱,同时,利用三简谐振子耦合模型计算了在不同入射角度下,腔模同时和重空穴激子模、轻空穴激子模耦合所形成的三支腔极化激元的能量,以及腔模、重空穴激子模、轻空穴激子模分别在三支腔极化激元中所占的权重,结果表明随着入射角的增加腔极化激元的高能支和两个低能支之间存在明显的反交叉现象,同时,腔模和重空穴激子模、轻空穴激子模在腔极化激元中所占的权重呈现增加或减小的趋势 关键词： 半导体微腔 腔极化激元 激子     

Test of the all-optical control of wave-particle duality of cavity photons by ordinary photodetection

The principle of complementarity refers to the ability of quantum entities to behave as particles or waves under different experimental conditions. We present a proposal for the experimental observation of the ultrafast all-optical control of the wave-particle duality of light. The device is constituted by a three-level quantum emitter strongly coupled to a microcavity (MC) and can be realized by exploiting a great variety of systems, ranging from atomic physics and semiconductor quantum dots to intersubband polaritons and Cooper pair boxes. The wavelike or particlelike behavior of MC photons can be probed by simply measuring the cavity output photon rate after excitation with pairs of phase-locked weak pulses with precise arrival times.     

Spin rings in bistable planar semiconductor microcavities

A remarkable feature of exciton-polaritons is the strongly spin-dependent polariton-polariton interaction, which has been predicted to result in the formation of spin rings in real space [Shelykh, Phys. Rev. Lett. 100, 116401 (2008)]. Here we experimentally demonstrate the spin bistability of exciton polaritons in an InGaAs-based semiconductor microcavity under resonant optical pumping. We observe the formation of spin rings whose size can be finely controlled in a spatial scale down to the micrometer range, much smaller than the spot size. Demonstration of optically controlled spin patterns in semiconductors opens way to the realization of spin logic devices and spin memories.     

Dynamics of a parametric exciton-polariton oscillator in a microcavity

We study the dynamics of parametric oscillations of polaritons in a microcavity that consists of a periodic conversion of a pair of pump polaritons into polaritons of signal and idle modes and vice versa. The period and amplitude of oscillations considerably depend on the initial polariton density, the initial phase difference, and the resonance detuning. We show that there is a possibility of phase controlling the polariton dynamics in the microcavity.     

Effect of quantizing magnetic field on the spectrum and damping of polaritons in double two-dimensional electronic systems

Nonradiative (surface and bulk) polaritons in a semiconductor structure composed of two heterojunctions GaAs/Al_xGa_1?x As are investigated under the integer quantum Hall effect (IQHE) conditions. The dispersive, polarization, and energy characteristics of these polaritons are determined including energy dissipation in the two-dimensional electron semiconductor layers. The phase and group velocities of surface and bulk polaritons are shown to be quantized under the IQHE conditions. It is found that resonance coupling of two surface polariton modes may occur in double GaAs/Al_xGa_1?x As heterojunctions. Possible experimental observation of nonradiative polaritons is discussed.     

A novel frequency encoded all optical logic gates exploiting polarization insesensitive four wave mixing in semiconductor optical amplifier, filtering property of ADD/DROP multiplexer and non-linearity of reflective semiconductor amplifier

All optical logic gates exploiting polarization independent four wave mixing in semiconductor optical amplifier (SOA), filtering property of ADD/DROP multiplexer (ADM) and non-linearity in reflective semiconductor optical amplifier (RSOA) have been proposed. The logic gates proposed are polarization independent which ensures hardware simplicity and greater speed. The all optical frequency encoded logic gates NOT, OR, NOR, AND, NAND, X-OR, X-NOR are implemented which are very useful in optical computing ad signal processing, cryptography, etc. The logic gates proposed have the advantages that there is no intensity loss dependent problem, and are polarization and temperature insensitive.