QUANTUM MANYBODY SYSTEMS
WHAT ARE THEY?

Quantum manybody systems are system made of several interacting particles, sometimes an infinite number of them. The most striking feature of these systems is that their properties are very different from the properties of the particles they are made of, in the words of one of the most famouse condesed matter physicist and Nobel laureate P. W. Anderson: "more is different". This feature is not a prerogative of quantum systems; there are examples of this difference between the physics of the microscopic components and a large system made of them already in the classical world. The most evident daily example is the transition from different phases of matter such as the water to ice one. When the rules of quantum mechanics are at play the effects become even more spectacular. Some of the most famous, as well as beautiful, examples BoseEinstein condensation, superconductivity and superradiance.

OUR RESEARCH

We develop methods to study the dynamics of manybody quantum systems such as ultracold atoms, small molecular junctions, nanoclusters. Our approach is based on the nonequilibrium Green's function theory together with the development of manybody perturbation theory techniques to treat interactions from a microscopic picture. We have developed a library and a set of numerical codes to solve the Dyson equation for the singleparticle Green's function. The Dyson equation in the nonequilibrium Green's function formally has the same importance of the Schroedinger equation for the wave function for the case of a single particle. We use this approach to study the outofequilibrium properties of different manybody quantum systems such as ultracold gases, transport in nanosystems, and excitonic systems. We are continuosly looking for new systems to develop new manybody perturbation approaches, compare them with other numerical and / or analytical approaches and enlarge our numerical library which we plan to make available to other researchers.
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