Thomas Weiss (N2 PhD student) under the supervision of Nikolay Gippius and Gérard Granet has obtained the** best thesis prize of DFH/UFA** which has been delivered to him by Mrs. Ambassador of Germany in Paris.

Hugo Flayac (N2 PhD student), supervised by G. Malpuech, has obtained the **Best Young Researcher Award of Clermont-Ferrand (Prix Jeune Chercheur 2013)**.

#### Nature Physics 9, 275 (2013)

**Macroscopic quantum self-trapping and Josephson oscillations of exciton-polaritons**

*M. Abbarchi, A. Amo, V.G. Sala, D.D. Solnyshkov, H. Flayac, L. Ferrier, I. SAgnes, E. Galopin, A. Lemaitre, G. Malpuech, J. Bloch*

The coupling of two macroscopic quantum states through a tunnel barrier gives rise to Josephson phenomena such as Rabi oscillations, the a.c. and d.c. effects, or macroscopic self-trapping, depending on whether tunnelling or interactions dominate. Nonlinear Josephson physics was first observed in superfluid helium and atomic condensates, but it has remained inaccessible in photonic systems because it requires large photon–photon interactions. Here we report on the observation of nonlinear Josephson oscillations of two coupled polariton condensates confined in a photonic molecule formed by two overlapping micropillars etched in a semiconductor microcavity. At low densities we observe coherent oscillations of particles tunnelling between the two sites. At high densities, interactions quench the transfer of particles, inducing the macroscopic self-trapping of polaritons in one of the micropillars. The finite lifetime results in a dynamical transition from self-trapping to oscillations with π phase. Our results open the way to the experimental study of highly nonlinear regimes in photonic systems, such as chaos or symmetry-breaking bifurcations.

#### Nature Communications 4, 2313 (2013)

**Polariton condensation in solitonic Gap states in a one dimensional periodic potential**

*D. Tanese, H. Flayac, D. Solnyshkov, A. Amo, A. Lemaitre, E. Galopin, R. Braive, P. Senellart, I. Sagnes, G. Malpuech, J. Bloch*

Manipulation of nonlinear waves in artificial periodic structures leads to spectacular spatial features, such as generation of gap solitons or onset of the Mott insulator phase transition. Cavity exciton–polaritons are strongly interacting quasiparticles offering large possibilities for potential optical technologies. Here we report their condensation in a one-dimensional microcavity with a periodic modulation. The resulting mini-band structure dramatically influences the condensation process. Contrary to non-modulated cavities, where condensates expand, here, we observe spontaneous condensation in localized gap soliton states. Depending on excitation conditions, we access different dynamical regimes: we demonstrate the formation of gap solitons either moving along the ridge or bound to the potential created by the reservoir of uncondensed excitons. We also find Josephson oscillations of gap solitons triggered between the two sides of the reservoir. This system is foreseen as a building block for polaritonic circuits, where propagation and localization are optically controlled and reconfigurable.

#### Phys. Rev. Lett. 110, 196406 (2013)

**From Excitonic to Photonic Polariton Condensate in a ZnO-Based Microcavity**

*Feng Li, L. Orosz, O. Kamoun, S. Bouchoule, C. Brimont, P. Disseix, T. Guillet, X. Lafosse, M. Leroux, J. Leymarie, M. Mexis, M. Mihailovic, G. Patriarche, F. Réveret, D. Solnyshkov, J. Zuniga-Perez, and G. Malpuech*

We report exciton-polariton condensation in a new family of fully hybrid ZnO-based microcavity demonstrating the best-quality ZnO material available (a bulk substrate), a large quality factor (∼4000) and large Rabi splittings (∼240 meV). Condensation is achieved between 4 and 300 K and for excitonic fractions ranging between 17% and 96%, which corresponds to a tuning of the exciton-polariton mass, lifetime, and interaction constant by 1 order of magnitude. We demonstrate mode switching between polariton branches allowing, just by controlling the pumping power, to tune the photonic fraction by a factor of 4.

#### Phys. Rev. Lett. 110, 236601 (2013)

**Realization of a Double-Barrier Resonant Tunneling Diode for Cavity Polaritons**

*H. S. Nguyen, D. Vishnevsky, C. Sturm, D. Tanese, D. Solnyshkov, E. Galopin, A. Lemaître, I. Sagnes, A. Amo, G. Malpuech, and J. Bloch*

We report on the realization of a double-barrier resonant tunneling diode for cavity polaritons, by lateral patterning of a one-dimensional cavity. Sharp transmission resonances are demonstrated when sending a polariton flow onto the device. We show that a nonresonant beam can be used as an optical gate and can control the device transmission. Finally, we evidence distortion of the transmission profile when going to the high-density regime, signature of polariton-polariton interactions. Editor's Suggestion + Viewpoint

#### Phys. Rev. Lett. 110, 246404 (2013)

**Skyrmion Formation and Optical Spin-Hall Effect in an Expanding Coherent Cloud of Indirect Excitons**

*D. V. Vishnevsky, H. Flayac, A. V. Nalitov, D. D. Solnyshkov, N. A. Gippius, and G. Malpuech*

We provide a theoretical description of the polarization pattern and phase singularities experimentally evidenced recently in a condensate of indirect excitons [H. High et al., Nature 483, 584 (2012)]. We show that the averaging of the electron and hole orbital motion leads to a comparable spin-orbit interaction for both types of carriers. We demonstrate that the interplay between a radial coherent flux of bright indirect excitons and the Dresselhaus spin-orbit interaction results in the formation of spin domains and of topological defects similar to Skyrmions. We reproduce qualitatively all the features of the experimental data and obtain a polarization pattern as in the optical spin-Hall effect despite the different symmetry of the spin-orbit interactions.

#### Phys. Rev. Lett. 110, 035303 (2013)

**Topological Wigner Crystal of Half-Solitons in a Spinor Bose-Einstein Condensate**

*H. Terças, D. D. Solnyshkov, and G. Malpuech*

We consider a one-dimensional gas of half-solitons in a spinor Bose-Einstein condensate. We calculate the topological interaction potential between the half-solitons. Using a kinetic equation of the Vlasov-Boltzmann type, we model the coupled dynamics of the interacting solitons. We show that the dynamics of the system in the gaseous phase is marginally stable and spontaneously evolves toward a Wigner crystal.

#### Phys. Rev. Lett. 110, 016404 (2013)

**Transmutation of skyrmions to half-solitons driven by the nonlinear optical spin-Hall effect**

*H. Flayac, D. Solnyshkov, I.A. Shelykh, G. Malpuech.*

We show that the spin domains, generated in the linear optical spin Hall effect by the analog of spin-orbit interaction for exciton polaritons, are associated with the formation of a Skyrmion lattice. In the nonlinear regime, the spin anisotropy of the polariton-polariton interactions results in a spatial compression of the domains and in a transmutation of the Skyrmions into oblique half-solitons. This phase transition is associated with both the focusing of the spin currents and the emergence of a strongly anisotropic emission pattern.