Quantum fluids of light
This research line aims at the fundamental understanding and active control of quantum fluids of light in nonlinear optical systems. In the presence of effective photon-photon interactions induced by the optical nonlinearity of the medium, a many-photon system can behave collectively as a quantum fluid with a number of novel features stemming from its intrinsically nonequilibrium nature. In the last decade, a rich variety of photon hydrodynamical effects has been theoretically predicted and soon observed, from the superfluid flow around a defect at low speeds to the appearance of a Mach-Cherenkov cone in a supersonic flow (fig.1), to the hydrodynamic formation of topological excitations such as quantized vortices and dark solitons at the surface of large impenetrable obstacles. Aspecially intriguing physics appears in the presence of external potentials, e.g. periodic ones (fig.2)
So far, our activity has mostly focused on a specific class of semiconductor systems (planar semiconductor microcavities in the strong light-matter coupling regime having cavity polaritons as elementary excitations), but the very concept of quantum fluids of light applies to a broad spectrum of systems, ranging from bulk nonlinear crystals, to atomic clouds embedded in optical fibers and cavities, to photonic crystal cavities, to superconducting quantum circuits based on Josephson junctions. In the last few years, we have begun to actively extend our interest to several of these systems, with very promising experimental perspectives.
Another direction of experimental development concerns strongly correlated photon gases and new effects stemming from artificial gauge fields for photons. For sufficiently strong nonlinearities, photon blockade is effective to make photons impenetrable particles. In spatially extended geometries, this is expected to lead to novel quantum phases of the photon fluid, with interesting applications to quantum technologies.
All details on this research line can be found in the recent review paper co-authored by the PI (Carusotto and Ciuti, RMP2013) as well as in the several popular science articles written for, e.g., EPN and Il Nuovo Saggiatore.
This research line is developing in close collaboration with theoretical groups at several international institutions, including Paris 7 and Antwerp universities, SNSin Pisa, ETHZurich. The Trento group is also involved in collaborations with many experimental groups, both local at Trento University and international, including LKB at Paris 6 and LPNin Marcoussis (near Paris) . These collaborations are supported by the Provincia di Trento (Grande Progetto “SiQuro”)and by the EU (FET-Proactive project “AQuS”).
Theoretical and experimental images showing the transition towards a superfluid state in a fluid of light (taken from Amo et al., Nature Physics 2009)
Experimental image of the polariton bands in a honeycomb lattice, showing linear dispersion at the Dirac points (from Jacqmin et al., PRL 2014)