Soliton Instabilities and Vortex Street Formation in a Polariton Quantum Fluid

Abstract

Exciton polaritons have been shown to be an optimal system in order to investigate the properties of bosonic quantum fluids. We report here on the observation of dark solitons in the wake of engineered circular obstacles and their decay into streets of quantized vortices. Our experiments provide a timeresolved access to the polariton phase and density, which allows for a quantitative study of instabilities of freely evolving polaritons. The decay of solitons is quantified and identified as an effect of disorderinduced transverse perturbations in the dissipative polariton gas. DOI: 10.1103/PhysRevLett.107.245301 PACS numbers: 67.10.Jn, 03.75.Lm, 71.36.+c, 78.67.Àn Perturbations of quantum fluids can lead to the creation of solitary waves called solitons resulting from the compensation between dispersion and particle interaction. In the particular case of repulsive interaction, dark solitons are created. These density depressions move in the fluid while keeping a constant shape and they are characterized by a phase jump across the density minimum. Since the first theoretical prediction [1], dark solitons have been studied and then observed in a variety of systems such as nonlinear lattices [2], thin magnetic films [3], and complex plasma [4]. They have attracted considerable interest especially in the field of nonlinear optics [5], because of their consequent use in communication devices (i.e., optical fibers [6]), and in atomic Bose-Einstein condensation (BEC) [7]. As quantized vortices [8][9][10], dark solitons are BEC excitations, which arise spontaneously upon the phase transition. As such, they are clear evidences for the onset of a quantum behavior and powerful tools to understand BEC instabilities. Controlling these instabilities is of crucial importance for the development of optoelectronic devices based on quantum fluids in which stable regimes and structures are required. Dark solitons are considered as the dispersive and nonlinear analog of shock waves of supersonic motion [11]. The creation of solitons by phase imprinting in BEC has been reported [12,13], triggering a growing interest in their hydrodynamic formation and stability of solitons.In this Letter we report on the observation of hydrodynamic oblique dark solitons in a 2D polariton fluid and the formation of quantized vortex streets. Polaritons are bosonic quasiparticles arising from the strong coupling between quantum well excitons and photons in semiconductor microcavities. Because of their small effective mass and their strong nonlinearity, they have turned out to be an optimal system in order to investigate the properties of a bosonic quantum fluid. Polaritons can undergo BEC [14] and, by virtue of their nonequilibrium nature, they are accompanied with the spontaneous appearance of quantized vortices [15]. With the demonstration of polariton superfluidity [16,17] much effort has been performed to better understand the nature of different turbulences arising from the breakdown of this fascinating state of matter. Recently, the hydrodynam...

Four-wave mixing excitations in a dissipative polariton quantum fluid

“…More than this, some of the most interesting dynamics observed in polariton condensates result from nonequilibrium. [15][16][17] Stabilization of polariton superflows by dissipation has even been predicted. 18 Strong-coupling regime brings another original aspect to the physics of microcavities: two polariton modes, sharing the same photonic and excitonic components can coexist in the cavity.…”

Robustness and observability of rotating vortex lattices in an exciton-polariton condensate

“…As such, these systems are capable of spatial and temporal pattern formation similar to that exhibited by lasers. 20,21 Quantized vortices 3,7,[9][10][11][12][13][14]17 and persistent currents 9 as well as soliton dynamics [16][17][18] have been observed in polariton condensates. Spatial patterns have been seen to arise spontaneously in both one 8 and two 15,19 dimensions.…”

“…Solid-state condensates exhibit striking fundamental differences from traditional quantum fluids such as atomic Bose gases and superfluid liquid helium. Much recent interest [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] has been devoted to exciton-polaritons, which exist as normal modes of strongly coupled excitons and photons in semiconductor microcavities. Due to the short lifetime of the quasiparticles, these condensates exist in a dynamic balance between pumping and decay rather than in true thermal equilibrium.…”

“…10,14 Most of the models that have been successfully and extensively used to describe pattern formation in polariton condensates are based on the complex Ginzburg-Landau equation (CGLE), which is also used in the theory of lasers and thus illustrates the similarities between the two systems. Such models have been applied to vortex nucleation and motion, 17,[23][24][25][26] spatial density modulations, 15,27 solitons, 16,17,23 and vortex lattices. [28][29][30][31] Various different modifications of this model have been considered, such as including separate dynamics of the reservoir or modeling processes of thermal relaxation.…”

Phase-Controlled Bistability of a Dark Soliton Train in a Polariton Fluid

“…While their excitonic component provides significant repulsive interactions, the fast escape of photons out of the microcavity makes polaritons an intrinsically open-dissipative system, requiring continuous wave pumping to achieve a steady state. A number of quantum fluid effects have been studied in semiconductor microcavities, including superfluidity [12], diffusive Goldstone modes [13], Bogoliubov excitation spectrum [14], solitary bright waves [15,16], and the hydrodynamic nucleation of quantized vortices [17,18] and dark solitons [7,8].In addition to the possibility of in-situ and timeresolved imaging of the fluid dynamics, a remarkable feature of driven-dissipative systems is that a resonant drive allows setting the local phase of the wavefunction [11]. It is then possible to externally manipulate the boundary conditions and impose a controlled phase pattern across a polariton fluid.…”