Experiments

Theory of bose-einstein condensates, cold atomic gases and quantum fluids

Since the experimental realization of BEC in 1995 the study of ultracold atomic gases has become a wide and fascinating field of physics involving hundreds of researchers in many laboratories around the world.
This field lies at the heart of quantum mechanics and has grown along with many developments of high interdisciplinary value. It benefits from the large variety of atomic species which can be used to reach the quantum degenerate regime and from all of the techniques available for manipulating atoms with light, and with electric and magnetic forces. The investigation of atomic quantum gases opens new horizons for both fundamental and applied research, starting from the basic laws which govern systems made of few or many particles, and leading to quantum control, interferometry, precise measurements, quantum simulations, etc..
The physics of Bose-Einstein condensates and ultracold gases represents an outstanding example of scientific research characterized by experimentalists and theorists working side by side, making progresses as a result of fruitful collaborations.
Ultracold gases are the archetype of a wider class of systems known as quantum fluids. They are dilute and clean; they can be confined in different 3D, 2D and 1D geometries; the interaction between particles can be tuned from very weak to very strong. This is why the theory of these gases is so rich. It is also interdisciplinary, many key concepts being used in different contexts as well, such as solid state physics, superconductors, superfluid helium, neutron stars, but also in systems of photons and more exotic particles. The theoretical activity in Trento ranges from the description of dilute Bose gases using Gross-Pitaevskii theory to the implementation of more advanced many-body approaches for strongly correlated systems and interacting Fermi gases. Both equilibrium and dynamic properties are investigated at zero and at finite temperatures. Particular attention is devoted to superfluid and quantum coherence effects, quantum mixtures, long range interactions, magnetic properties, low dimensionality and optical lattices.
Another research line aims at investigating the novel properties of light in systems with large optical nonlinearities where the many photons forming the light field display a rich collective dynamics. As compared to standard many-body systems like helium and ultracold atoms, new perspectives are opened by the intrinsic non-equilibrium nature of the photon gas. A number of material systems can be used for these studies, from nonlinear optical crystals in the strong light-matter coupling regime to semiconductor microcavities and even circuit QED devices in the microwave domain. Superfluidy of light has been experimentally demonstrated at LKB in Paris, following a previous Trento-Paris prediction: a fluid of dressed photons (exciton-polaritons) was sent against a structural defect of a microcavity. While at high speeds a variety of perturbations appear (Cerenkov cones, dark solitons, vortices), at low speeds no excitation is created in the fluid. The long-term objectives of this research line are to explore what new exotic states of matter can be generated in quantum fluids of light and, conversely, how many-body effects in the fluid of light may reflect into new applications to quantum photonic technologies.

Numerical simulation of a dark soliton oscillation in a Fermi gas at unitarity in harmonic confinement.

Pictorial view of the mechanism for generating second sound in a Fermi superfluid at unitarity in harmonic trap.