Manni, Francesco

Tuesday April 18, 2013
Time: 10:30
Place: ETH Science City, HPF G 6
Host: Atac Imamoglu

The Penrose-Onsager criterion and spinor topological defects in Exciton-Polariton condensates

Francesco Manni
Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne

In the recent years, polariton systems have attracted a growing interest from a broad scientific community in reason of the rich physics and wide range of observations that have been assessed by several groups. In particular, the successful demonstration of Bose-Einstein condensation (BEC) of polaritons in planar semiconductor microcavities triggered a series of studies that brought to the observation of a variety of striking phenomena, ranging from polariton superfluidity and Josephson oscillations to the identification and study of quantized vortical entities. Although most of the phenomenology is remarkably similar to that observed in cold atoms and other Bose-degenerate quantum systems, the intrinsic non-equilibrium nature of polaritons brought relevant elements of novelty both in the experimental techniques and in the theoretical picture underlying the observed phenomena, extending the meaning of well-known and established theoretical concepts.
The general definition for BEC was first proposed by Penrose and Onsager back in 1956, in terms of the so-called “Penrose-Onsager criterion”. This criterion was conceived and successfully applied to equilibrium BEC while, on the contrary, an experimental validation of the Penrose-Onsager criterion in the framework of non-equilibrium condensates had never been provided and represented an intriguing open question for the quantum fluid community. We performed quantum tomography on one-dimensional polariton condensates and implement a test of the Penrose-Onsager criterion for BEC in the framework of non-equilibrium systems.
On the other hand, further investigations were carried on in the framework of spinor polariton condensates, devoted to unveiling quantized spin vortices, predicted to occur in such systems but yet not experimentally observed. Spin vortices were identified in our polariton condensed system and characterized by full reconstruction of the condensate vector order parameter.