Letter abstract
Nature Physics 5, 805 - 810 (2009)
Published online: 20 September 2009 | doi:10.1038/nphys1364
Subject Categories: Condensed-matter physics | Optical physics | Quantum physics
Superfluidity of polaritons in semiconductor microcavities
Alberto Amo1, Jérôme Lefrère1, Simon Pigeon2, Claire Adrados1, Cristiano Ciuti2, Iacopo Carusotto3, Romuald Houdré4, Elisabeth Giacobino1 & Alberto Bramati1
Superfluidity, the ability of a quantum fluid to flow without friction, is one of the most spectacular phenomena occurring in degenerate gases of interacting bosons. Since its first discovery in liquid helium-4 (refs 1, 2), superfluidity has been observed in quite different systems, and recent experiments with ultracold trapped atoms have explored the subtle links between superfluidity and Bose–Einstein condensation3, 4, 5. In solid-state systems, it has been anticipated that exciton–polaritons in semiconductor microcavities should behave as an unusual quantum fluid6, 7, 8, with unique properties stemming from its intrinsically non-equilibrium nature. This has stimulated the quest for an experimental demonstration of superfluidity effects in polariton systems9, 10, 11, 12, 13. Here, we report clear evidence for superfluid motion of polaritons. Superfluidity is investigated in terms of the Landau criterion and manifests itself as the suppression of scattering from defects when the flow velocity is slower than the speed of sound in the fluid. Moreover, a 
erenkov-like wake pattern is observed when the flow velocity exceeds the speed of sound. The experimental findings are in quantitative agreement with predictions based on a generalized Gross–Pitaevskii theory12, 13, and establish microcavity polaritons as a system for exploring the rich physics of non-equilibrium quantum fluids.
- Laboratoire Kastler Brossel, Université Pierre et Marie Curie, Ecole Normale Supérieure et CNRS, UPMC Case 74, 4 place Jussieu, 75252 Paris Cedex 05, France
- Laboratoire Matériaux et Phénomènes Quantiques, UMR 7162, Université Paris Diderot-Paris 7 et CNRS, 75013 Paris, France
- BEC-CNR-INFM and Dipartimento di Fisica, Universita di Trento, I-38050 Povo, Italy
- Institut de Photonique et d'Electronique Quantique, Ecole Polytechnique Fédérale de Lausanne, Station 3, CH-1015 Lausanne, Switzerland
Correspondence to: Alberto Amo1 e-mail: alberto.amo@spectro.jussieu.fr
Correspondence to: Alberto Bramati1 e-mail: bramati@spectro.jussieu.fr
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