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We study, theoretically and numerically, the onset and development of modulational instability in an incoherently pumped spatially homogeneous polariton condensate. Within the framework of mean-field theory, we identify regimes of modulational instability in two cases: (1) strong feedback between the condensate and reservoir, which may occur in scalar condensates, and (2) parametric scattering in the presence of polarization splitting in spinor condensates. In both cases we investigate the instability-induced textures in space and time including nonequilibrium dynamics of phase dislocations and vortices. In particular we discuss the mechanism of vortex destabilization and formation of spiraling waves. We also identify the presence of topological defects, which take the form of half-vortex pairs in the spinor case, giving an "eyelet" structure in intensity and dipole-type structure in the spin polarization. In the modulationally stable parameter domains, we observe formation of the phase defects in the process of condensate formation from an initially spatially incoherent low-density state. In analogy to the Kibble-Zurek-type scaling for nonequilibrium phase transitions, we find that the defect density scales with the pumping rate. [ABSTRACT FROM AUTHOR]

We observe a bistability in an electrically driven polariton condensate, which is manifested by a memory dependent threshold characteristic. In contrast to the polariton bistabilities previously observed in resonantly optically pumped microcavities, our effect occurs under nonresonant electric pumping and is triggered by the current injection scheme. We explain the origin of the bistability by a dependence of the electron-hole tunneling lifetime on the carrier density in the embedded quantum wells. The field screening effect creates a positive feedback loop, which yields the bistable behavior of the condensate. We develop a rate-equation-based model which qualitatively explains the occurrence of the hysteresis under current injection, its reduction with increased magnetic field, and the absence of bistability under optical pumping. [ABSTRACT FROM AUTHOR]

We present a time-resolved photoluminescence (PL) study in real and momentum space of a polariton condensate switch in a quasi-one-dimensional semiconductor microcavity. The polariton flow across the ridge is gated by excitons inducing a barrier potential due to repulsive interactions. A study of the device operation dependence on the power of the pulsed gate beam obtains a satisfactory compromise for the on-off signal ratio and switching time of the order of 0.3 and ~50 ps, respectively. The opposite transition is governed by the long-lived gate excitons, consequently, the off-on switching time is ~200 ps, limiting the overall operation speed of the device to ~3 GHz. The experimental results are compared to numerical simulations based on a generalized Gross-Pitaevskii equation, taking into account incoherent pumping, decay, and energy relaxation within the condensate. [ABSTRACT FROM AUTHOR]

The role of quasicylindrical waves and surface plasmon polaritons in beam shaping with resonant nanogratings is investigated. It is shown that the field on the grating surface can be strongly influenced by plasmons and quasicylindrical waves in the infrared. A method that combines far-field measurements with the fast Fourier transform to map the field amplitude at the grating surface is demonstrated. For samples with a small degree of geometric asymmetry, it is shown that the imaginary part of the transform (with null zeroth-order component) can better map the amplitude of the resonant surface waves than the full complex-valued transform. Our results will impact the study, design, and footprint of resonant nanogratings. [ABSTRACT FROM AUTHOR]

We study the dynamics of polariton condensate wave trains that propagate along a quasi-one-dimensional waveguide. Through the application of tuneable potential barriers the propagation can be reflected and multiple reflections used to confine and store a propagating state. Energy-relaxation processes allow the delayed relaxation into a long-living coherent ground state. Aside from the potential routing of polariton condensate signals, the system forms an AND-type logic gate compatible with incoherent inputs. [ABSTRACT FROM AUTHOR]

Polariton condensates have proved to be model systems to investigate topological defects, as they allow for direct and nondestructive imaging of the condensate complex order parameter. The fundamental topological excitations of such systems are quantized vortices. In specific configurations, further ordering can bring the formation of vortex lattices. In this work we demonstrate the spontaneous formation of ordered vortical states, consisting in geometrically self-arranged vortex-antivortex pairs. A mean-field generalized Gross-Pitaevskii model reproduces and supports the physics of the observed phenomenology. [ABSTRACT FROM AUTHOR]

We present a time-resolved study of energy relaxation and trapping dynamics of polariton condensates in a semiconductor microcavity ridge. The combination of two nonresonant, pulsed laser sources in a GaAs ridge-shaped microcavity gives rise to profuse quantum phenomena where the repulsive potentials created by the lasers allow the modulation and control of the polariton flow. We analyze in detail the dependence of the dynamics on the power of both lasers and determine the optimum conditions for realizing an all-optical polariton condensate transistor switch. The experimental results are interpreted in the light of simulations based on a generalized Gross-Pitaevskii equation, including incoherent pumping, decay, and energy relaxation within the condensate. [ABSTRACT FROM AUTHOR]

We report on pure-quantum-state polariton condensates in optical annular traps. The study of the underlying mechanism reveals that the polariton wave function always coalesces in a single pure quantum state that, counterintuitively, is always the uppermost confined state with the highest overlap with the exciton reservoir. The tunability of such states combined with the short polariton lifetime allows for ultrafast transitions between coherent mesoscopic wave functions of distinctly different symmetries, rendering optically confined polariton condensates a promising platform for applications such as many-body quantum circuitry and continuous-variable quantum processing. [ABSTRACT FROM AUTHOR]

We show theoretically that an open-dissipative polariton condensate confined within a trapping potential and driven by an incoherent pumping scheme gives rise to bistability between odd and even modes of the potential. Switching from one state to the other can be controlled via incoherent pulsing which becomes an important step towards construction of low-powered optoelectronic devices. The origin of the effect comes from modulational instability between odd and even states of the trapping potential governed by the nonlinear polariton-polariton interactions. [ABSTRACT FROM AUTHOR]

We report on a remarkable effect of pseudospin precession on the collective motion of exciton-polaritons in a microresonator coherently driven by a linearly polarized pump. In particular, we show that hexagonal patterns can undergo a spontaneous symmetry breaking of their polarization and start a uniform motion in the plane of the resonator. Similar to the optical spin Hall effect, this becomes possible due to a spin-orbit interaction induced by a longitudinal-transverse splitting (TE-TM splitting) of the photonic resonator mode. We derive a simple analytical expression for the drift velocity of the patterns. [ABSTRACT FROM AUTHOR]

We propose a scheme of continuous tunable THz emission based on dipolaritons, mixtures of strongly interacting cavity photons and direct excitons, where the latter are coupled to indirect excitons via tunneling. We investigate the property of multistability under continuous wave (CW) pumping, and the stability of the solutions. We establish the conditions of parametric instability, giving rise to oscillations in density between the direct-exciton and indirect-exciton modes under CW pumping. In this way, we achieve continuous and tunable emission in the THz range in a compact single-crystal device. We show that the emission frequency can be tuned in a certain range by varying an applied electric field and pumping conditions. Finally, we demonstrate the dynamic switching between different phases in our system, allowing rapid control of THz radiation. [ABSTRACT FROM AUTHOR]

A polariton condensate transistor switch is realized through optical excitation of a microcavity ridge with two beams. The ballistically ejected polaritons from a condensate formed at the source are gated using the 20 times weaker second beam to switch on and off the flux of polaritons. In the absence of the gate beam the small built-in detuning creates a potential landscape in which ejected polaritons are channelled toward the end of the ridge where they condense. The low-loss photonlike propagation combined with strong nonlinearities associated with their excitonic component makes polariton-based transistors particularly attractive for the implementation of all-optical integrated circuits. [ABSTRACT FROM AUTHOR]

We report on the observation of spin whirls in a radially expanding polariton condensate formed under nonresonant optical excitation. Real space imaging of polarization- and time-resolved photoluminescence reveals a spiralling polarization pattern in the plane of the microcavity. Simulations of the spatiotemporal dynamics of a spinor condensate reveal the crucial role of polariton interactions with a spinor exciton reservoir. Harnessing spin-dependent interactions between the exciton reservoir and polariton condensates allows for the manipulation of spin currents and the realization of dynamic collective spin effects in solid-state systems. [ABSTRACT FROM AUTHOR]

We present a practical scheme for creating topological polaritons in garden-variety systems based, for example, on zinc-blende semiconductor quantum wells. Our proposal requires a moderate magnetic field and a potential landscape which can be implemented, e.g., via surface acoustic waves or patterning. We identify indirect excitons in double quantum wells as an appealing alternative for topological states in exciton-based systems. Topological polaritons and indirect excitons open a new frontier for topological states in solid-state systems, which can be directly probed and manipulated while offering a system with nonlinear interactions. [ABSTRACT FROM AUTHOR]

We consider a quantum well embedded in a zero-dimensional microcavity with a subwavelength grated mirror, where the x-linearly polarized exciton mode is strongly coupled to the cavity photon, while y-polarized excitons remain in the weak-coupling regime. Under incoherent optical or electric pumping, we demonstrate polariton bistability associated with parametric scattering processes. Such bistability is useful for constructing polaritonic devices with optical or electrical incoherent pumping. [ABSTRACT FROM AUTHOR]

We show that in a nonequilibrium system of an exciton-polariton condensate, where polaritons are generated from incoherent pumping, a ring-shaped pump allows for stationary vortex memory elements of topological charge m = 1 or m = - 1. Using simple potential guides we can choose whether to copy the same charge or invert it onto another spatially separate ring pump. Such manipulation of binary information opens the possibility of a new type of processing using vortices as topologically protected memory components. [ABSTRACT FROM AUTHOR]

We investigate spin transport through polarization-resolved spectroscopy by propagating polariton condensates in a quasi-one-dimensional microcavity ridge along macroscopic distances. Under circularly polarized, continuous-wave, nonresonant excitation, a sinusoidal precession of the spin in real space is observed whose phase depends on the emission energy. The experiments are compared with simulations of the spinor-polariton condensate dynamics based on a generalized Gross-Pitaevskii equation, modified to account for incoherent pumping, decay, and energy relaxation within the condensate. [ABSTRACT FROM AUTHOR]