Relaxation kinetics for temperature and degeneracy of microcavity polaritons

We apply a semi-classical Boltzmann kinetics for a gas of laser-pulse excited microcavity polaritons taking into account their mutual interaction and their interaction with acoustic phonons. Fitting the temporally evolving polariton distribution above the ground state with a Bose–Einstein distribution, we find the evolution of the temperature and the degeneracy parameter, i.e. the ratio of the chemical potential to the thermal energy. Studying the relaxation in particular for GaAs microcavities we compare our results with recent measurements by Deng et al. In agreement with the experiment we find that the lattice temperature can be reached and that the degeneracy of the condensed gas holds up to 60–80 ps provided a detuning of the cavity mode is applied which increases the exciton component of the lower-branch polaritons and thus their scattering rates.     

Optical properties of microcavity polaritons

This work contains a theoretical analysis of the optical properties of semiconductor quantum wells embedded in planar Fabry-Perot microcavities. In particular, the properties of the system in correspondence to the excitonic transition are studied by means of the polariton formalism. The polariton states in microcavities are derived and the polar-iton dispersion is presented. Particular emphasis is put on the existence of two well distinct regimes depending on the exciton and cavity parameters: strong coupling and weak coupling regime. The main experimental results are reviewed and compared with the prediction of the theory. After the polariton states have been characterized, the optical response of the system is discussed, with particular attention to the photoluminescence measurements. The polariton formation and relaxation through phonon scattering and the effect of the exciton inhomogeneous broadening are considered and, finally, a phe-nomenological model for the polariton photoluminescence spectra is presented.     

Long-range spin-qubit interaction mediated by microcavity polaritons

We study the optically induced coupling between spins mediated by polaritons in a planar microcavity. In the strong-coupling regime, the vacuum Rabi splitting introduces anisotropies in the spin coupling. Moreover, due to their photonlike mass, polaritons provide an extremely long spin coupling range. This suggests the realization of two-qubit all-optical quantum operations within tens of picoseconds with spins localized as far as hundreds of nanometers apart.     

Characteristics of exciton polaritons in a ZnO microcavity

We have investigated the characteristics of exciton polaritons in a ZnO microcavity with HfO₂/SiO₂ distributed Bragg reflectors. The results of the angle-resolved reflectance spectra were analyzed by calculating the cavity polariton dispersions with a phenomenological Hamiltonian for the coupling between the cavity photon and three kinds of excitons labeled A, B, and C peculiar to ZnO. The vacuum-Rabi-splitting energy is estimated to be ∼80 meV. The reflectance dips originating from the cavity polaritons shift to lower energy side with an increase in temperature. We discuss the temperature dependence of the cavity-polariton energies of the ZnO microcavity on the basis of the phenomenological Hamiltonian taking account of the temperature dependence of the exciton energies with Varshni’s law.     

Time resolved scattering relaxation mechanisms of microcavity polaritons

We study the polariton relaxation dynamics for different scattering mechanisms as: Phonon and electron scattering procesess. The relaxation polariton is obtained at very short times by solving the Boltzman equation. Instead of the well-known relaxation process by phonons, we show that the bottleneck effect relaxes to the ground state more efficiently at low pump power intensity when the electron relaxation process is included. In this way, we clearly demonstrate that different relaxation times exist, for which any of these two mechanism is more efficient to relax the polariton population to the ground state.     

Dynamics of microcavity polaritons in the Markovian limit

A master equation for the reduced density matrix of the microcavity polaritons coupled with the reservoir of high energy excitons is derived. It is allowed both the polaritons and the excitons to be self-interacting systems. Long time asymptotic properties of the polariton population is studied in the whole range of the reservoir temperatures and the corresponding decoherence effects are reported.     

Quantum wire polaritons

Summary Using a nonlocal susceptibility with cilindrical symmetry as computed from the microscopic theory, we obtain the exciton-polariton modes in quantum wires, where the translational symmetry is preserved in one direction only. Resonant polaritons, with a finite radiative lifetime, result for , while wire polaritons with infinite radiative lifetime result fork _‖>k ₀. Dispersion laws and lifetimes are given for all values ofk _‖, and the separation between the longitudinal and the nonlongitudinal mode is obtained. Numerical examples are given for GaAs/Ga_1−x Al _x As quantum wires.     

Bose condensation of exciton polaritons in an optical microcavity

Two methods are considered for producing traps for exciton polaritons in an optical microcavity with an embedded quantum well. The first method for controlling polaritons consists in producing a polariton trap governed by the longitudinal confinement of photons. Traps of this type can be created using an optical microcavity with a variable width. In traps of the second type, the exciton confinement is ensured by a weak potential that is applied to a quantum well with excitons or when this well is subjected to an inhomogeneous deformation. The behavior of a two-component Bose condensate of photons and excitons is analyzed theoretically. The Bose condensate is described by the coupled system of equations of the Gross-Pitaevskii type. The approximate wave functions and the spatial profiles of coupled photon and exciton condensates are obtained.     

Dynamic stark effect in strongly coupled microcavity exciton polaritons

We present experimental observations of a nonresonant dynamic Stark shift in strongly coupled microcavity quantum well exciton polaritons-a system which provides a rich variety of solid-state collective phenomena. The Stark effect is demonstrated in a GaAs/AlGaAs system at 10?K by femtosecond pump-probe measurements, with the blueshift approaching the meV scale for a pump fluence of 2 mJ?cm^{-2} and 50?meV red detuning, in good agreement with theory. The energy level structure of the strongly coupled polariton Rabi?doublet remains unaffected by the blueshift. The demonstrated effect should allow generation of ultrafast density-independent potentials and imprinting well-defined phase profiles on polariton condensates, providing a powerful tool for manipulation of these condensates, similar to dipole potentials in cold-atom systems.     

Bragg diffraction of microcavity polaritons by a surface acoustic wave

Bragg scattering of polaritons by a coherent acoustic wave is mediated and strongly enhanced by the exciton states resonant with the acoustic and optic fields in the intraband and interband transitions, respectively. In this case, in contrast with conventional acousto-optics, the resonantly enhanced Bragg spectra reveal the multiple orders of diffracted light. For polaritons in GaAs microcavities driven by a surface acoustic wave of nu(SAW)=1 GHz and I(ac)< or approximately 100 W/cm(2) the main acoustically induced band gap can be as large as Delta(MC)(ac) approximately equal to 0.6 meV and the Bragg replicas up to n=3 can be observed.     

Coloured noise controlled dynamics of nonlinear polaritons in semiconductor microcavity

The coloured noise induced escape rate from the lower energy stable state of a driven nonlinear microcavity oscillator has been investigated by means of quasi-classical kinetic equations. We show that for coloured, i.e. narrow-band, relatively intense noise, the escape time is controlled by the interplay of two mechanisms: the noise induced drift and adiabatic regular shift of the oscillator state towards unstable saddle point. The cross-over between these mechanisms takes place in a particular range of the driving field intensity values, depending on the ratio between the oscillator damping and the coloured noise spectrum width. The dependence of the transition rate on the noise correlation time is analyzed for wide range of correlation time values. The article is published in the original.     

Towards thermal equilibrium in the Bose-Einstein condensation of microcavity polaritons

By comparing a kinetic and a thermal-equilibrium theory of polariton Bose-Einstein condensation, we study under what conditions the dynamical condensation under steady-state non-resonant pumping can approach thermal equilibrium. In particular, we study the dependence on two material parameters: the vacuum-field Rabi-splitting and the polariton radiative lifetime. When increasing the Rabi splitting, condensation takes place under strong non-equilibrium conditions, with dominating quantum fluctuations. Increasing the polariton lifetime above 10 ps at moderate Rabi splitting, instead, produces a quasi-equilibrium condensate at low exciton density, consistently with the picture of a weakly interacting Bose gas.     

One dimensional confinement of microcavity polaritons using non-piezoelectric surface acoustic waves

We demonstrate the manipulation of microcavity polaritons using tunable one-dimensional potentials formed by non-piezoelectric surface acoustic waves (SAWs). We compare the modulation of polaritons by piezoelectric and non-piezoelectric SAWs and show that the latter outperform the former for high acoustic powers. We directly show the formation of mini-Brillouin zones due to the lateral modulation with the periodicity of the SAW as well as the flattening of the lowest dispersion curve due to polariton confinement, showing the formation of polariton wires.     

Bragg polaritons: strong coupling and amplification in an unfolded microcavity

Periodic incorporation of quantum wells inside a one-dimensional Bragg structure is shown to enhance coherent coupling of excitons to the electromagnetic Bloch waves. We demonstrate strong coupling of quantum well excitons to photonic crystal Bragg modes at the edge of the photonic band gap, which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg polariton branches are in good agreement with the theory and allow demonstration of Bragg polariton parametric amplification.     

Exciton polaritons in a one-and-a-half-wave algan microcavity: Results of mathematical modeling

Several manifestations of exciton polaritons formed as a result of the interaction of a light wave with a microresonator containing quantum wells in a one-and-a-half-wave AlGaN microcavity are considered using approaches typical of mathematical modeling. The electric field of the light wave in the microcavity and the angular dispersion of the polariton branches are obtained using the transfer-matrix method.     

Optical Tamm state polaritons in a quantum well microcavity with gold layers

A new type of cavity polariton,the optical Tamm state(OTS) polariton,is proposed to be realized by sandwiching a quantum well(QW) between a gold layer and a distributed Bragg reflector(DBR).It is shown that OTS polaritons can be generated from the strong couplings between the QW excitons and the free OTSs.In addition,if a second gold layer is introduced into the bottom of the DBR,two independent free OTSs can interact strongly with the QW excitons to produce extra OTS polaritons.     

Spin dynamics of a vortical condensate of exciton polaritons in a GaAs microcavity

The temporal dynamics of a spinor exciton-polariton condensate in a high-quality anisotropic GaAs microcavity under pulsed resonant excitation with light possessing a nonzero orbital angular momentum is investigated. The phenomenon of spatial separation of the spin components of the polariton condensate upon pumping with a coherent superposition of two beams with opposite circular polarizations and orbital angular momenta is observed. The key factors for the observation of this effect are the lateral anisotropy of the microcavity that causes a splitting between the linear components of the polariton ground state and the occurrence of opposite orbital angular momenta for the two spin components of the condensate. The experimental results are in qualitative agreement with the theoretical model of the phenomenon developed in JETP Lett. 104, 827 (2016).     

Probability density tomography of microcavity polaritons confined in cylindrical traps of various sizes

We present the optical tomography of the probability density of microcavity polaritons, confined in three dimensions by cylindrical traps of various sizes. Collecting the photoluminescence emitted by the quasimodes under continuous nonresonant laser excitation, we reconstruct a three dimensional mapping of the photoluminescence, from which we can extract the spatial distribution of the confined states at any energy. We discuss the impact of the confinement shape and size on the probability density patterns.