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Register a new userPseudo-conservative dynamics of coupled polariton condensates
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Open-dissipative systems obeying parity-time ($mathcal{PT}$) symmetry are capable of demonstrating oscillatory dynamics akin to the conservative systems. In contrast to limit cycle solutions characteristic of nonlinear systems, the $mathcal{PT}$-symmetric oscillations form a continuum of non-isolated orbits. However, precise sculpturing of the real potential and the gain-loss spatial profiles required for establishing of the $mathcal{PT}$-symmetry is practically challenging. The optical devices, such as lasers, exhibit relaxation dynamics and do not operate as the $mathcal{PT}$-symmetric systems. Here we demonstrate how these constraints can be overcome. We predict that a pair of optically trapped polariton condensates (a polariton dimer) can be excited and operated in the oscillating regime typical of the isolated systems. This regime can be realized in the presence of both dissipative and conservative coupling between the condensates and can be maintained at an arbitrary external pump intensity. Every orbit is characterised by a frequency comb appearing in the spectrum of a dimer in the presence of the conservative nonlinearity. Our results pave the way for the creation of the optical computing devices operating under the constant-wave external pumping.
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The phase and the frequency of an exciton polariton condensate excited by a nonresonant pump can be efficiently manipulated by an external coherent light. Being tuned close to the resonance with the condensate eigenfrequency, the external laser light imposes its frequency to the condensate and locks its phase, thereby manifesting a synchronization effect. The conditions of formation of the phase synchronized regime are determined. The synchronization of a couple of closely spaced polariton condensates by a spatially uniform coherent light is examined. At the moderate strength of the coherent driving the synchronization is accompanied by the appearance of symmetry-breaking states of the polariton dyad, while these states are superseded by the symmetric state at the high-intensity driving. By employing a zero-dimensional model of coupled dissipative oscillators with both dissipative and conservative coupling, we study the bifurcation scenario of the symmetry-breaking state formation.
The generalized Gross-Pitaevskii equation (gGPE) is an effective phenomenological description for the dynamics of incoherently pumped exciton-polariton condensates. However, a brute force numerical simulation of the gGPE provides little physical insight into condensate formation under arbitrary pumping configurations, and is demanding in terms of computational resources. We introduce in this paper a modal description of polariton condensation under incoherent pumping of arbitrary spatial profile, based on eigenmodes of the non-Hermitian generator of the linearized dynamics. A pump-dependent basis is then introduced to formulate a temporal coupled-mode theory that captures condensate dynamics in the presence of all nonlinear interactions. Simulations using a single set of modes for a given pumping and trapping configuration agree very well with a full integration of the gGPE in diverse dynamical regimes, supporting the validity of this modal description, while also providing a speedup in simulation times.
The drag of half-light half-mater quasiparticles, exciton-polaritons, by an electric current is a peculiar mechanism of light-matter interaction in solids. While an ideal superfluid is protected from being dragged by its zero viscosity, here we argue that the state of the superfluid polariton condensate formed by a non-resonant optical pumping can be controlled by the electric current. The proposed mechanism is based on the stimulated relaxation of moving uncondensed excitons dragged by the electric current. The stimulated relaxation process favors the formation of a moving condensate in a quantum state that is characterised by the lowest condensation threshold. We also show that the electron-mediated inelastic scattering of the reservoir excitons to the condensate leads to the transfer of a non-zero mean momentum to the electron gas thus contributing to the electric current. We predict the generation of circular electric currents in a micropillar cavity in the presence of a nonresonant laser pumping at normal incidence.
We investigate the thermal robustness of traveling polariton condensates. We create remote condensates that have never been in contact, and study their interference in momentum space, when they travel with the same velocity, by means of time-resolved photoluminescence. We determine the condensed to thermal, uncondensed polariton fraction, which shows a gradual decay with increasing temperature, and obtain the critical temperature for the Bose-Einstein-like condensate (BEC) phase transition. We tentatively compare our experimental findings with theoretical models, developed for atomic condensates, to describe the condensates coherence fading with temperature.
We study the stability of collective amplitude excitations in non-equilibrium polariton condensates. These excitations correspond to renormalized upper polaritons and to the collective amplitude modes of atomic gases and superconductors. They would be present following a quantum quench or could be created directly by resonant excitation. We show that uniform amplitude excitations are unstable to the production of excitations at finite wavevectors, leading to the formation of density-modulated phases. The physical processes causing the instabilities can be understood by analogy to optical parametric oscillators and the atomic Bose supernova.
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