Cavity-polariton Systems Research Articles

Mid-Infrared Intersubband Cavity Polaritons in Flexible Single Quantum Well

Strong and ultrastrong coupling between intersubband transitions in quantum wells and cavity photons have been realized in mid-infrared and terahertz spectral regions. However, most previous works employed a large number of quantum wells on rigid substrates to achieve coupling strengths reaching the strong or ultrastrong coupling regime. In this work, we experimentally demonstrate ultrastrong coupling between the intersubband transition in a single quantum well and the resonant mode of photonic nanocavity at room temperature. We also observe strong coupling between the nanocavity resonance and the second-order intersubband transition in a single quantum well. Furthermore, we implement for the first time such intersubband cavity polariton systems on soft and flexible substrates and demonstrate that bending of the single quantum well does not significantly affect the characteristics of the cavity polaritons. This work paves the way to broaden the range of potential applications of intersubband cavity polaritons including soft and wearable photonics.

Ultrafast acoustic switching of an optically pumped cavity polariton system in the bistable regime

Nonequilibrium transitions are investigated in a plane exciton-polariton system with complex acousto-optical excitation: stationary resonant optical excitation of polaritons along the normal to the surface of the resonator and picosecond strain pulses causing reversible exciton energy perturbations. It is shown that acoustic pulses can be used for ultrafast switching of the optical response of a bistable polariton system. Switching is experimentally implemented in a high-Q GaAs microcavity.

Ultrafast strain-induced switching of a bistable cavity-polariton system

In the reported experiment, a picosecond strain pulse induces a sharp transition between the steady states in a bistable cavity-polariton system. The strain pulse of 10-ps duration, generated in the GaAs substrate and injected into a high-$Q$ GaAs/AlAs microcavity, modulates the exciton resonance energies of the embedded quantum wells and correspondingly of the polariton resonances. When the microcavity is pumped by a laser with the photon energy slightly above the lower-polariton resonance, the strain-induced energy shift triggers the irreversible switching of the bistable polariton system from the lower to the upper state. This transition is accompanied by an instant increase of the optical emission from the microcavity by more than an order of magnitude.

Spinor soliton arrays in cavity-polariton wires

Theoretical and numerical study is performed of bright solitons in a resonantly driven cavity-polariton system with linear coupling of two spin components. Together with repulsive Coulomb interaction of polaritons with parallel spins, such coupling involves spontaneous breakdown of spin symmetry. Solitons originate under the joint action of a continuous-wave excitation and spatially local short-term pulse. Due the symmetry breaking, solitons exhibit two intensity peaks with opposite spins which are separated in space. Here we predict spontaneous formation of large soliton arrays with alternating spins. The number of intensity peaks is found to gradually increase in the course of soliton propagation, resulting in turbulent field states.

Self-shaping of cavity-polariton systems created by resonant broadband excitation

The dynamics of a pure low polariton (LP) system created by resonant broadband excitation in a wide range of wave vectors was investigated in a high-$Q$ GaAs-based microcavity. The LP system is shown to inherit the high spatial coherence from the laser pulse and does not lose it during decay. As a result, its dynamics is well controlled by the spatial and momentum distributions of photons in the exciting pulse and described by the Gross-Pitaevskii equations. In particular, the purely dynamic formation of the highly populated coherent LP state was implemented at the LP band bottom in the cavity excited in a large spot by converging ps-long Gaussian laser pulses when the active region of the cavity is in front of its waist. The formed state is found to persist for several picoseconds until the LP-LP repulsion leads to the creation of high-energy LPs dissipating from the ground state with high velocities.

Polariton Chimeras: Bose-Einstein Condensates with Intrinsic Chaoticity and Spontaneous Long-Range Ordering.

The system of cavity polaritons driven by a plane electromagnetic wave is found to undergo the spontaneous breaking of spatial symmetry, which results in a lifted phase locking with respect to the driving field and, consequently, in the possibility of internal ordering. In particular, periodic spin and intensity patterns arise in polariton wires; they exhibit strong long-range order and can serve as media for signal transmission. Such patterns have the properties of dynamical chimeras: they are formed spontaneously in perfectly homogeneous media and can be partially chaotic. The reported new mechanism of chimera formation requires neither time-delayed feedback loops nor nonlocal interactions.

Controlled spin pattern formation in multistable cavity–polariton systems

Theoretical studies are performed of planar cavity–polariton systems under resonant optical excitation. We show that if the cavity is spatially anisotropic, the polariton spin is highly sensitive to the pump polarization direction, which can be used to modulate the circular polarization of the output light. In particular, when the right- and left-circular components of the incident wave have equal intensities and mutually opposite angular momenta, the pump has strictly linear yet angle-dependent polarization and as such brings about a periodic angular variation of the polariton spin. Free motion of polaritons is the other factor determining the shape of the cavity-field distribution. Such externally driven and highly tunable spin patterns represent a counterpart of spin shaping in nonresonantly excited Bose–Einstein condensates of cavity polaritons.

Towards spin turbulence of light: Spontaneous disorder and chaos in cavity-polariton systems

Recent advances in nanophotonics have brought about coherent light sources with chaotic circular polarization; a low-dimensional chaotic evolution of optical spin was evidenced in laser diodes. Here we propose a mechanism that gives rise to light with a spatiotemporal spin chaos resembling turbulent states in hydrodynamics. The spin-chaotic radiation is emitted by exciton polaritons under resonant optical pumping in arbitrarily sized planar microcavities, including, as a limiting case, pointlike systems with only three degrees of freedom. The underlying mechanism originates in the interplay between spin symmetry breakdown and scattering into pairs of Bogolyubov excitations. As a practical matter, it opens up the way for spin modulation of light on the scale of picoseconds and micrometers.

All-optical control of three-photon spectra and time asymmetry in a strongly coupled cavity polariton system

Manipulating the nature of photons emission is one of the basic tasks in quantum optics and photonics. The ever growing list of quantum applications requires a robust means of controlling the strongly coupled coherent interaction of photons and matter. Here, we investigate three-photon transmission spectra in a strongly coupled cavity polariton system and show that the correlation functions and transmitted photon stream can be optically manipulated. The dynamics of single photons and photon pairs at the polariton resonances can be changed by light from a single external coupling laser. At the “dark-state polariton,” three-photon transmission is a perfectly coherent field in contrast to the strong photon-bunching behavior of a typical cavity quantum electrodynamics system. When the detuned probe light is tuned to the “bright polariton,” the light exhibits a dramatic photon antibunching effect. Remarkably, the Fano-resonant asymmetric three-photon transmission caused by the interference between the dressed states leads to a new quantum feature that is strongly nonclassical (the third-order correlation function g(3)(0, 0) ≪ 1) and has a wide and tunable bandwidth. The dependence of the intrinsic third-order correlation and time symmetry of the photon stream on the controlled parameters is also examined. Strongly nonclassical, all-optically controllable multi-photon dynamics are very important for future quantum devices and metrology.

Blowup dynamics of coherently driven polariton condensates: Experiment

We report an experimental verification of the recent prediction that sharp transitions between steady states in multistable cavity-polariton systems are mediated by intermode parametric scattering that triggers the accumulation of energy and, hence, lowers the threshold at the cost of extending the transition latency period [S. S. Gavrilov, Phys. Rev. B 90, 205303 (2014)]. The time-resolved measurements are performed using a high-$Q$ GaAs microcavity pumped slightly above the lower polariton level at normal incidence.

Transient optical parametric oscillations in resonantly pumped multistable cavity polariton condensates

Transitional processes accompanying switches between steady states in multistable cavity polariton systems are studied experimentally in a low-symmetry high-$Q$ microcavity under resonant optical excitation at normal incidence. We show that the establishment of a high-energy polariton state is influenced by an optical parametric oscillation. Therefore, the emission spectrum reveals the energy-separated signal-idler pairs in both spin components. Accordingly, the time dependencies of the polariton emission exhibit oscillations whose periods correspond to the spectral positions of the scattered states. Thus, the sharp transitions between the steady states of a no-equilibrium polariton condensate enable one to visualize the near-condensate eigenmodes and explore their spectral and spin properties depending on the condensate amplitude and average spin.

A hybrid-structure of a cavity polariton system and an optical-ring

Abstract We demonstrate a hybrid-structure of a ZnO polariton system and an optical-ring in this work. In this structure, we create room-temperature polariton condensate in the ZnO nanowire. The coherent light emission from the polariton condensate is coupled to the ring, and the coherence of the coupled light is examined by Young interference experiment using a photoluminescence mapping system. Finally, the efficiency of the waveguide of the coupled light in the ring has been carefully discussed.

Blowup dynamics of coherently driven polariton condensates

Based on the Gross-Pitaevskii equations, it is predicted that a repulsive interaction provides a way for a two-dimensional polariton condensate to accumulate energy in spite of dissipation under above-resonance optical pumping. The energy can be accumulated over a time much longer than the polariton lifetime, resulting in the state in which the blueshift of the polariton level compensates the mismatch of the pump frequency. The process starts when the field density reaches the parametric scattering threshold that is inversely proportional to the polariton lifetime. Although the increase in energy may be arbitrarily slow in the beginning, it is followed by a blowup. This scenario applies to the case of transitions between steady states in multistable cavity-polariton systems. There is a tradeoff between the latency of the transitions and the pump power.

Polariton-polariton interactions in microcavities under a resonant 10 to 100 picosecond pulse excitation

Experimental studies have been performed of the nonequilibrium transitions in multistable cavity-polariton systems under 10 ps long pulsed excitation, i.e., within nearly the shortest time scale necessary for the multistability to be revealed in GaAs-based microcavities. The experiments were aimed to determine the ratio of the strengths of the pair interactions between polaritons with parallel and antiparallel spins, which also was the question raised in a number of recent studies. We show that in contrast to the cases of continuous-wave or nanosecond long pumping conditions, in the fast pulse regime the system is not affected by the excitonic reservoir. The interaction between polaritons with opposite spins is definitely attractive at a nearly zero detuning of exciton and photon modes; as a result, optical response can be essentially multistable at a linearly polarized excitation. With increasing pulse duration up to 100 ps, the reservoir can start manifesting itself in a reduction of the spin multistability.

Spin multistability of cavity polaritons in a magnetic field

Spin transitions are studied theoretically and experimentally in a resonantly excited system of cavity polaritons in a magnetic field. Weak pair interactions in this boson system make possible fast and massive spin flips occurring at critical amplitudes due to the interplay between amplitude dependent shifts of eigenstates and the Zeeman splitting. Dominant spin of a condensate can be toggled forth and back by tuning of the pump intensity only, which opens the way for ultra-fast spin switchings of polariton condensates on a picosecond timescale.

Polariton multistability and fast linear-to-circular polarization conversion in planar microcavities with lowered symmetry

The multistability of cavity-polariton systems with lowered symmetry (e.g., in laterally strained microcavities) allows implementing a few picoseconds long switching from linear to almost circular polarization of the cavity transmission under a resonant linearly polarized optical pump with slowly changing intensity. This effect has been observed in a high-Q GaAs microcavity using spectrally narrow 70 ps long pump pulses.

Multistability of cavity exciton polaritons affected by the thermally generated exciton reservoir

Until now, the generation of an excitonic reservoir in a cavity polariton system under quasi-resonant pumping has always been neglected. We show that in microcavities having a small Rabi splitting (typically GaAs cavities with a single quantum well), this reservoir can be efficiently populated by polariton-phonon scattering. We consider the influence of the exciton reservoir on the energy shifts of the resonantly pumped polariton modes. We show that the presence of this reservoir effectively reduces the spin anisotropy of the polariton-polariton interaction, in agreement with recent experimental measurements, where the multistability of cavity polaritons has been analyzed

Bistability and nonequilibrium transitions in the system of cavity polaritons under nanosecond-long resonant excitation

The polarization dependence of nonequilibrium transitions in a multistable cavity-polariton system is studied under a nanosecond long resonant optical excitation at the normal and magic angle incidences with various polarizations of the pump beam. The temporal correlations between the frequency, intensity, and optical polarization of the intra-cavity field, which all undergo sharp threshold-like changes due to the spin dependent interaction of cavity polaritons, are visualized. The observed dynamics cannot be reproduced within the conventional semi-classical model based on the Gross-Pitaevskii equations. To explain the observed phenomena, it is necessary to take into account the unpolarized exciton reservoir which brings on additional blueshift of bright excitons, equal in the $\sigma^+$ and $\sigma^-$ polarization components. This model explains the effect of polarization instability under both pulsed and continuous wave resonant excitation conditions, consistently with the spin ring pattern formation that has recently been observed under Gaussian shaped excitation.

Nonlinear Terahertz Emission in Semiconductor Microcavities

We consider the nonlinear terahertz emission by the system of cavity polaritons in the regime of polariton lasing. To account for the quantum nature of terahertz-polariton coupling, we use the Lindblad master equation approach and demonstrate that quantum microcavities reveal a rich variety of nonlinear phenomena in the terahertz range, including bistability, short terahertz pulse generation, and terahertz switching.

Kinetics of stimulated polariton scattering in planar GaAs microcavities resonantly excited with a linearly polarized light

Nonequilibrium transitions in the cavity polariton system are investigated under nanosecond-long pulsed excitation with linearly polarized light (TE or TM modes) near the magic angle. The main objective is to clarify the influence of the polarization-dependent properties of the polariton-polariton interaction on (i) instabilities in a driven lower polariton mode and (ii) the temporal hysteresis effects in the kinetics of the scattered polariton population. The driven mode retains the polarization of the exciting pulse and exhibits instabilities typical of the scalar (``spinless'') polariton system excited with circularly polarized light. No increase in the instability threshold for the driven mode and, as a consequence, no polarization multistability discussed for the spinor polariton system [N. A. Gippius et al., Phys. Rev. Lett. 98, 236401 (2007)] is observed. Polarization of the scattering signal at the zero wave vector and that of the driven mode are mutually perpendicular, due to the polarization dependence of the exciton-exciton interaction. At the same time, at pump intensities well above the threshold of stimulated scattering, the signal exhibits a markable decrease (up to 25%) of the polarization degree during the pulse transmission.