We realize bistability in the spinor of polariton condensates under nonresonant optical excitation and in the absence of biasing external fields. Numerical modeling of the system using the Ginzburg-Landau equation with an internal Josephson coupling between the two spin components of the condensate qualitatively describes the experimental observations. We demonstrate that polariton spin bistability strongly depends on the condensate's overlap with the exciton reservoir by tuning the excitation geometry and sample temperature. We obtain noncollapsing bistability hysteresis loops for a record range of sweep times, [10 μs, 1 s], offering a promising route to spin switches and spin memory elements.
We realize bistability in the spinor of polariton condensates under nonresonant optical excitation and in the absence of biasing external fields. Numerical modeling of the system using the Ginzburg-Landau equation with an internal Josephson coupling between the two spin components of the condensate qualitatively describes the experimental observations. We demonstrate that polariton spin bistability strongly depends on the condensate's overlap with the exciton reservoir by tuning the excitation geometry and sample temperature. We obtain noncollapsing bistability hysteresis loops for a record range of sweep times, [10 μs, 1 s], offering a promising route to spin switches and spin memory elements.
We theoretically investigate a spinor polariton condensate under nonresonant pumping, based on driven-dissipative Gross-Pitaevskii equations coupled to the rate equation of a spin-unpolarized reservoir. We find the homogeneous polariton condensate can transit from the spin-unpolarized phase, where it is linearly polarized, to the spin-polarized phase, where it is elliptically polarized, depending on the cross-spin versus same-spin interactions and the linear polarization splitting. In both phases, we study elementary excitations using Bogoliubov approach, in a regime where the decay rate of total exciton density in reservoir crosses over from the slow to the fast limit. Depending on reservoir parameters, the global-phase mode can be either diffusive or gapped. By contrast, the relative-phase mode always possesses a gapped energy, undamped in the spin-unpolarized phase but weakly damped in the spin-polarized phase. In the spin-unpolarized phase, both modes are linearly polarized despite pumping and decay. However, in the spin-polarized phase, the mode polarization can be significantly affected by the reservoir and depends strongly on the circular polarization degree of the condensate. Interestingly, we demonstrate that the ``ghost'' branch of the Bogoliubov spectrum of the relative-phase mode can be visualized in the photoluminescence emission, distinguishable from that of the global-phase mode and thus allowing for experimental observation, when the spinor polariton condensate is elliptically polarized.
It is shown that a condensate of microcavity exciton-polaritons exhibits bistability between its two orthogonal linearly polarized components for varying nonresonant excitation power.A non-Hermitian splitting of these components results in two parity-symmetric fixed-point solutions of opposite polarization, making up the hysteresis branches.These solutions correspond to the lowest threshold linearly polarized mode, which dominates at low pump powers, and a cross-polarized mode, which appears due to nonlinear pinning at higher excitation powers.The spin symmetry of the solutions extends the nonresonant bistable operation of polariton condensates to the entire equatorial plane of the Poincaré sphere.The results pave the way towards development of tailored bistable, linearly polarized, coherent sources of light.
Polaritons are quasiparticles resulting from the strong coupling between photons and excitons embedded in a semiconductor microcavity. The exciton component of polaritons provides strong nonlinear interactions, while their photonic counterpart facilitates long range coherence. Moreover, polaritons carry a pseudospin that can be accessed through the polarization state of the emitted light, and brings up spinor related nonlinear effects. This study aims at in-depth investigation of the noise related phenomena in polariton system. First, a series of experiments of polariton bistability and multistability are performed to deepen our knowledge about the effect of the biexciton creation and polariton-polariton interaction on multistable regimes in exciton polaritons. Then, using an external Gaussian noise, the polariton transition rate between two stable states of a polariton bistability is characterized. It is shown that the external noise specifications, intensity and correlation time, can efficiently modify the polariton Kramers time and residence time. We also discuss the performance of the bistable behaviour in steady state regime in terms of experimental acquisition time compared to the noise-assisted residence time. In the next part, taking advantage of polariton bistability and spin-trigger regime, we have evidenced two different types of stochastic resonance. Intensity stochastic resonance and spinor stochastic resonance. We have shown that the synergic interplay between intensity fluctuations and external modulated signal, imprinted on the DC component of the driving field, can enhance the coherent processing of an input signal buried in noise. Moreover, we evidence that, due to the exceptional spin properties of polaritons, a noisy modulated polarized input signal can drive the switching of a fully polarized polariton population. This effect unveils an original field of stochastic resonance which we called as spinor stochastic resonance. All experimental results are well reproduced by a model based on Gross-Pitaevskii equation. At the end, the influence of nonlinear interactions on polariton intensity fluctuations and probability distribution have been investigated.
We study the nonlinear dynamics of spinor exciton-polaritons in resonantly pumped microcavities. Using steady-state analysis and computing eigenfrequencies via Bogoliubov-like linearization, we show that multiple Hopf bifurcations beyond conventional bistability occur within specific power regimes and are not associated with stable solutions of the system. Owing to nonlinear excitonic interactions, these transitions occur at different pump powers during forward and backward pump sweeps, leading to pronounced hysteresis between fixed-point and limit-cycle states. In the spinor regime, multiple limit-cycle branches and associated dynamical hysteresis loops emerge due to the interplay of polarization coupling and spin-dependent nonlinearities. We show how the locations of the bifurcation points can be tuned by the pump frequency and other system parameters. Our results identify synchronization as the organizing principle underlying limit-cycle formation, dynamical hysteresis, and bifurcation cascades in driven spinor exciton-polariton microcavities.
The polarization dependence of nonequilibrium transitions in a multistable cavity-polariton system is studied under nanosecond-long resonant optical excitation at normal and magic angle incidences with various polarizations of the pump beam. The temporal correlations between the frequency, intensity, and optical polarization of the intracavity 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 semiclassical model based on the Gross-Pitaevskii equations. To explain the observed phenomena, it is necessary to take into account the unpolarized exciton reservoir that brings on an additional blue shift of bright excitons, the same for the ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ 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.
Abstract By adopting a mean-field Gross–Pitaevskii description of spinor polariton Bose–Einstein condensates under nonresonant pumping, we investigate the static and dynamical properties of dark–bright (DB) solitons. We derive the equation of motion for the center of mass of the DB solitons’ center analytically by using the Hamiltonian approach. The resulting equation captures how the combination of the open-dissipative character and the spin degrees of freedom of a polariton Bose–Einstein condensate affects the properties of DB solitons, i.e. DB solitons relax by blending with the background at a finite time. In this case, we also determine the lifetime of the DB solitons. Further numerical solutions of the modified dissipative two-component Gross–Pitaevskii equations are in excellent agreement with the analytical results. In the presence of the Langevin noise, we demonstrate that the DB solitons can still propagate for a long time, which is sufficient for their experimental observations within current facilities.