Abstract
Modulational instabilities play a key role in a wide range of nonlinear optical phenomena, leading e.g. to the formation of spatial and temporal solitons, rogue waves and chaotic dynamics. Here we experimentally demonstrate the existence of a modulational instability in condensates of cavity polaritons, arising from the strong coupling of cavity photons with quantum well excitons. For this purpose we investigate the spatiotemporal coherence properties of polariton condensates in GaAs-based microcavities under continuous-wave pumping. The chaotic behavior of the instability results in a strongly reduced spatial and temporal coherence and a significantly inhomogeneous density. Additionally we show how the instability can be tamed by introducing a periodic potential so that condensation occurs into negative mass states, leading to largely improved coherence and homogeneity. These results pave the way to the exploration of long-range order in dissipative quantum fluids of light within a controlled platform.
Highlights
Modulational instabilities are a widespread feature of nonlinear wave systems, whereby small perturbations get amplified and grow exponentially with time. They manifest in numerous branches of physics ranging from hydrodynamics [1] to nonlinear optics [2], plasma physics [3], and cold atom gases [4]
A homogeneous cold atom condensate becomes unstable in the presence of attractive interactions, which make the condensate collapse so as to minimize its Polaritons, arising from the strong coupling of quantum well excitons and cavity photons [27], are an appealing candidate to address this question
The physical mechanism of the polariton instability is expected to be independent of the dimensionality of the system [31]
Summary
Modulational instabilities are a widespread feature of nonlinear wave systems, whereby small perturbations get amplified and grow exponentially with time. When these effective interactions overcome the direct repulsive interactions between polaritons, the condensate is expected to enter a modulationally unstable regime [31] characterized by a turbulent steady state [29,30,32,33,34] This behavior strongly contrasts the collapse scenario of attractively interacting cold atom gases and is another intriguing example of the rich non-equilibrium physics of drivendissipative polariton condensates. When the cavities are spatially patterned into lattices so that condensation occurs in negative mass states, the modulational instability is suppressed, and all previous signatures of instability disappear: the condensates reach a stable steady state with high homogeneity and coherence This method for suppressing instabilities opens avenues for studying the rich phenomenology of drivendissipative condensates [36,37,38,39,40,41,42,43], such as Kardar–Parisi–Zhang (KPZ) universal scalings, in a controlled environment. Our proposal of using negative mass states to facilitate the establishment of long-range order could prove useful to achieve stable condensation in these novel platforms
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