107 research outputs found
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
Definition of the stimulated emission threshold in high- nanoscale lasers through phase-space reconstruction
Nanoscale lasers sustain few optical modes so that the fraction of
spontaneous emission funnelled into the useful (lasing) mode is high
(of the order of few 10) and the threshold, which traditionally
corresponds to an abrupt kink in the light in- light out curve, becomes
ill-defined. We propose an alternative definition of the threshold, based on
the dynamical response of the laser, which is valid even for lasers.
The laser dynamics is analyzed through a reconstruction of its phase-space
trajectory for pulsed excitation. Crossing the threshold brings about a change
in the shape of the trajectory and in the area contained in it. An unambiguous
definition of the threshold in terms of this change is shown theoretically and
illustrated experimentally in a photonic crystal laser
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
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