Polaritons, half-light half-matter mixed states arising from the strong coupling between excitons and photons in semiconductor microcavities, are composite bi-dimensional interacting bosons. They can manifest macroscopic quantum coherence effects at high temperatures (5-300 K) due to their very low mass. In particular, polaritons behave like a quantum fluid with specific properties coming from its intrinsic out of equilibrium nature, determined by the short polariton lifetime (some picoseconds)

In this talk, I will briefly review the superfluid and Cerenkov regimes [1, 2] in these systems, then I will discuss the formation of quantized vortex and dark solitons in a polariton quantum fluid interacting with a large obstacle [3, 4]. Finally, I will present the recent observation of dark half-solitons in a spinor polariton fluid [5].

In the last part of the talk, the possibility to generate vortex-antivortex lattices in a confined geometry will be discussed.

These results demonstrate that the polaritons are an ideal system for the study of the quantum fluid properties.

[1] A. Amo, D. Sanvitto, F. P. Laussy, D. Ballarini, et al., Nature 457, 291 (2009).

[2] A. Amo, J. Lefrère, S. Pigeon, C. Adrados, et al., Nature Phys. 5, 805 (2009).

[3] A. Amo, S. Pigeon, D. Sanvitto, V.G. Sala, R. Hivet, et al., Science, 332, 1167 (2011).

[4] D. Sanvitto, S. Pigeon, A. Amo, D. Ballarini, et al, Nature Photonics, 5, 610 (2011)

[5] R. Hivet, H. Flayac, D.D. Solnyshkov, D. Tanese et al. Nature Phys. 8, 724 (2012)