A. Amo

Bosonic Condensation and Disorder-Induced Localization in a Flat Band.

We report on the engineering of a nondispersive (flat) energy band in a geometrically frustrated lattice of micropillar optical cavities. By taking advantage of the non-Hermitian nature of our system, we achieve bosonic condensation of exciton polaritons into the flat band. Because of the infinite effective mass in such a band, the condensate is highly sensitive to disorder and fragments into localized modes reflecting the elementary eigenstates produced by geometric frustration. This realization offers a novel approach to studying coherent phases of light and matter under the controlled interplay of frustration, interactions, and dissipation.

Lasing in topological edge states of a one-dimensional lattice

Topology describes properties that remain unaffected by smooth distortions. Its main hallmark is the emergence of edge states localized at the boundary between regions characterized by distinct topological invariants. Because their properties are inherited from the topology of the bulk, these edge states present a strong immunity to distortions of the underlying architecture. This feature offers new opportunities for robust trapping of light in nano- and micrometre-scale systems subject to fabrication imperfections and environmentally induced deformations. Here, we report lasing in such topological edge states of a one-dimensional lattice of polariton micropillars that implements an orbital version of the Su–Schrieffer–Heeger Hamiltonian. We further demonstrate that lasing in these states persists under local deformations of the lattice. These results open the way to the implementation of chiral lasers in systems with broken time-reversal symmetry and, when combined with polariton interactions, to the study of nonlinear phenomena in topological photonics.Topologically protected lasing is reported in a lattice of polariton micropillars.

Probing a Dissipative Phase Transition via Dynamical Optical Hysteresis

We experimentally explore the dynamical optical hysteresis of a semiconductor microcavity as a function of the sweep time. The hysteresis area exhibits a double power law decay due to the influence of fluctuations, which trigger switching between metastable states. Upon increasing the average photon number and approaching the thermodynamic limit, the double power law evolves into a single power law. This algebraic behavior characterizes a dissipative phase transition. Our findings are in good agreement with theoretical predictions for a single mode resonator influenced by quantum fluctuations, and the present experimental approach is promising for exploring critical phenomena in photonic lattices.

Interaction-induced hopping phase in driven-dissipative coupled photonic microcavities

The Bose-Hubbard model (BHM) describes bosons hopping across sites and interacting on-site. Inspired by the success of BHM simulators with atoms in optical lattices, proposals for implementing the BHM with photons in coupled nonlinear cavities have recently emerged. Two coupled semiconductor microcavities constitute a model system where the hopping, interaction and decay of exciton polaritons—mixed light-matter quasiparticles—can be engineered in combination with site-selective coherent driving to implement the driven-dissipative two-site optical BHM. Here we explore the interplay of interference and nonlinearity in this system, in a regime where three distinct density profiles can be observed under identical driving conditions. We demonstrate how the phase acquired by polaritons hopping between cavities can be controlled through polariton-polariton interactions. Our results open new perspectives for synthesizing density-dependent gauge fields using polaritons in two-dimensional multicavity systems.

Surface-enhanced gallium arsenide photonic resonator with quality factor of 6 × 10 6

Gallium arsenide and related compound semiconductors lie at the heart of optoelectronics and integrated laser technologies. Shaped at the micro- and nanoscale, they allow strong interaction with quantum dots and quantum wells, and promise stunning optically active devices. However, gallium arsenide optical structures presently exhibit lower performance than their passive counterparts based on silicon, notably in nanophotonics, where the surface plays a chief role. Here, we report on advanced surface control of miniature gallium arsenide optical resonators using two distinct techniques that produce permanent results. One extends the lifetime of free carriers and enhances luminescence, while the other strongly reduces surface absorption and enables ultra-low optical dissipation devices. With such surface control, the quality factor of wavelength-sized optical disk resonators is observed to rise up to 6×106 at the telecom wavelength, greatly surpassing previous realizations and opening new prospects for gallium arsenide nanophotonics.

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

We use a one-dimensional polariton fluid in a semiconductor microcavity to explore the nonlinear dynamics of counterpropagating interacting Bose fluids. The intrinsically driven-dissipative nature of the polariton fluid allows us to use resonant pumping to impose a phase twist across the fluid. When the polariton-polariton interaction energy becomes comparable to the kinetic energy, linear interference fringes transform into a train of solitons. A novel type of bistable behavior controlled by the phase twist across the fluid is experimentally evidenced.

Theoretical study of stimulated and spontaneous Hawking effects from an acoustic black hole in a hydrodynamically flowing fluid of light

We propose an experiment to detect and characterize the analog Hawking radiation in an analog model of gravity consisting of a flowing exciton-polariton condensate. Under a suitably designed coherent pump configuration, the condensate features an acoustic event horizon for sound waves that at the semiclassical level is equivalent to an astrophysical black-hole horizon. We show that a continuous-wave pump-and-probe spectroscopy experiment allows to measure the analog Hawking temperature from the dependence of the stimulated Hawking effect on the pump-probe detuning. We anticipate the appearance of an emergent resonant cavity for sound waves between the pump beam and the horizon, which results in marked oscillations on top of an overall exponential frequency dependence. We finally analyze the spatial correlation function of density fluctuations and identify the hallmark features of the correlated pairs of Bogoliubov excitations created by the spontaneous Hawking process, as well as novel signatures characterizing the emergent cavity.

Polariton lasing in the edge states of an orbital SSH chain

Engineering orbital bands in photonic simulators (i.e., bands emerging from the coupling of 1φ0 orbitais) provides an excellent platform to study novel transport, and nonlinear and topological phenomena in solids [1]. For example, they allow studying flat bands in a honeycomb lattice [2], exotic edge states of topologically non-trivial orbital bands, orbital symmetry breaking [3], and orbital superfluidity [4]. Cavity polaritons are well-suited for implementing these simulators, because their photonic part allows coupling p- and higher photonic orbitals in extended lattices [3], while their excitonic part furnishes strong interactions that are required for investigating non-linear effects. In this work, we elaborate and demonstrate an orbital version of the well-known Su-Schrieffer-Heeger model (SSH) using p-bands in a zigzag chain of polariton micropillars (see Fig. (a)-(c)) and show polariton lasing in the topological edge states located at the ends of the chain. The demonstration of polariton lasing in topological edge states opens the way to the study of nonlinear transport in chiral states of topological insulators [5].

Buildup and decay of the coherence in a polariton condensate

We report the dynamics of a polariton condensate, created by a nonresonant light pulse, and the determination of its coherence buildup and decay. The time‐resolved experiments show clearly the interplay between the relevant quantities of polariton condensates: population, linewidth and polarization. A comparison with the results of a Lindblad master equation, describing the dynamics of the system coupled to a reservoir, demonstrates the importance of both the pulse shape and the flow of particles between the ground‐state and the reservoir in the build‐up of the coherence.

Observation of Quantum Hydrodynamic Effects in Microcavity Polaritons

We study the hydrodynamics of a coherent polariton fluid lasting for hundreds of picoseconds and moving inside of a semiconductor microcavity. The momentum of the polariton droplets can be well controlled by selecting the angle and energy of two excitation laser beams. We observe unique behaviours due to the quantum nature of the polariton states, such as the linearization of the polariton dispersion around the energy of the signal states, and the propagation at constant speed of the polariton fluids. The experiments have been realized making use of a new technique for the detection of images simultaneously resolved in time, energy and real‐ or reciprocal‐ space.