Unstable and stable regimes of polariton condensation

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.Comment: 7 pages, 5 figure

Nonlinear Polariton Fluids in a Flatband Reveal Discrete Gap Solitons

Phase frustration in periodic lattices is responsible for the formation of dispersionless flat bands. The absence of any kinetic energy scale makes flat band physics critically sensitive to perturbations and interactions. We report here on the experimental investigation of the nonlinear dynamics of cavity polaritons in the gapped flat band of a one-dimensional Lieb lattice. We observe the formation of gap solitons with quantized size and very abrupt edges, signature of the frozen propagation of switching fronts. This type of gap solitons belongs to the class of truncated Bloch waves, and had only been observed in closed systems up to now. Here the driven-dissipative character of the system gives rise to a complex multistability of the nonlinear domains generated in the flat band. These results open up interesting perspective regarding more complex 2D lattices and the generation of correlated photon phases.Comment: 6 pages, 4 figures + supplemental material (6 pages, 6 figures

Nonreciprocity and zero reflection in nonlinear cavities with tailored loss

International audienc

Designs on the popular : framings of general, universal and common culture in French educational policy

This article examines the culture-shaping strategies pursued through French educational policies. It traces the process through which the republican education system claimed legitimacy to bring all citizens into its universalising embrace, and to institute a form of national popular culture. At the same time, the article shows how specifications of esoterically ‘universal’ and ‘general’ curricular content were used to maintain barriers between elite and popular classes. The article then explores endeavours since the 1940s to delineate more democratically framed notions of ‘general’ or ‘common’ culture, and the difficulties that have accompanied the integration of such perspectives into mass secondary schooling since the 1960s. In particular, one sees in France persistent disjunctions between the ‘universal’ cultures carried by academic curricula and contemporary popular cultures and experience (though the balance of power between these poles has shifted in some respects)

Emergence of criticality through a cascade of delocalization transitions in quasiperiodic chains

7 pages, 4 figures + supplementary material (9 pages, 6 figures, 2 videos), comments are welcomeConduction through materials crucially depends on how ordered they are. Periodically ordered systems exhibit extended Bloch waves that generate metallic bands, whereas disorder is known to limit conduction and localize the motion of particles in a medium. In this context, quasiperiodic systems, which are neither periodic nor disordered, reveal exotic conduction properties, self-similar wavefunctions, and critical phenomena. Here, we explore the localization properties of waves in a novel family of quasiperiodic chains obtained when continuously interpolating between two paradigmatic limits: the Aubry-Andr\'e model, famous for its metal-to-insulator transition, and the Fibonacci chain, known for its critical nature. Using both theoretical analysis and experiments on cavity-polariton devices, we discover that the Aubry-Andr\'e model evolves into criticality through a cascade of band-selective localization/delocalization transitions that iteratively shape the self-similar critical wavefunctions of the Fibonacci chain. Our findings offer (i) a unique new insight into understanding the criticality of quasiperiodic chains, (ii) a controllable knob by which to engineer band-selective pass filters, and (iii) a versatile experimental platform with which to further study the interplay of many-body interactions and dissipation in a wide range of quasiperiodic models