Theory of many-body quantum systems, quantum information and computation

The Quantum group studies quantum entanglement and its implications in field theories and many-body systems. In the presence of a macroscopic number of elementary constituents - as is the case in statistical physics, condensed matter, or fundamental field theories - quantum correlations can generate exotic collective phenomena whose understanding requires the development of new ideas and theoretical tools.

In this context, the research activities of the Quantum group follow two directions. The first one is motivated by experimental advances in the physics of cold atoms, which have made it possible to observe new collective quantum behavior, making it urgent to develop new computational techniques and effective theories, especially in low dimensionality.

The second research direction is motivated by the fact that new experimental possibilities have facilitated the implementation of quantum computers and simulators with a large number of elementary components (qubits). Current prototypes of quantum computers are far from ideal, and theoretical effort is required both for understanding the physics of the quantum platforms used and for developing algorithms for current prototypes.

Finally, taking into account the social impact of quantum technologies, the Quantum group is also collaborating on teaching quantum physics at the high school and university levels.

 

Faculty members: Elisa Ercolessi, Marcello Dalmonte, Pierbiagio Pieri, Lorenzo Piroli

Research activities 

Quantum phase transitions of matter in low dimensions

The structure of the phase diagram of quantum matter in low dimensions is fixed by the properties of quantum correlations and entanglement. When combined with quantum information techniques, the use of effective field theories and of numerical algorithms (quantum Monte Carlo, Tensor Networks) allows for the study of phase transitions and the classification of phases in one-dimensional models with a vast range of both short and long range interactions, in static conditions as well as out of equilibrium. 

Critical phenomena, integrability and  entanglement

Conformal field theory and quantum integrability are very powerful tools for the study of 1+1 dimensional models that describe paradigmatic examples in condensed matter physics (e.g. the Ising model) as well as in field theory (e.g. the sine-Gordon model), by means of non-perturbative and exact techniques  Both at- and out-of-equilibrium, quantum correlations and entanglement exhibit universal properties that can be calculated by means of these techniques and can be used to characterize phase transitions and quantum phases of the system.

Quantum simulations of field theories

Systems of atoms/ions trapped in optical lattices yield experimental platforms in which it is possible to simulate the Hamiltonian of quantum field theories for both condensed matter and fundamental interactions in particles and gravity. By combining the theory of critical phenomena with numerical techniques which exploit the properties of quantum correlations and entanglement, such as DMRG and Tensor Networks, we study lattice field theory Hamiltonians (Schwingermodel for QED, gauge theories), by looking at non-perturbative aspects -such as confinement- or out-of-equilibrium phenomena -such as the string breaking mechanism.

Quantum computation and quantum machine learning

This activity develops along two complementary lines of research. The first one is about the connections between statistical mechanics, many body theory and quantum computing, mainly in connection with the problem of quantum error correction and the characterization of physical systems, such as trapped ions,  that can be used to implement quantum processors. The second deals with the possible use of classical algorithms for the study of quantum many body systems as well as that of quantum algorithms for machine learning and data analysis.

Quantum gases, superconductors, and BCS-BEC crossover

Trapped ultracold gases have recently allowed the experimental exploration of the BCS-BEC crossover (that is, the evolution that bridges the phenomenon of superconductivity to Bose-Einstein condensation), while raising at the same time several new theoretical problems. We address some of these challenges by combining many-body diagrammatic methods with the development of efficient algorithms for their numerical implementation. We use the same methods to also analyze new superconductors in condensed matter.

Quantum physics - teaching and social impact

In the era of the “second quantum revolution”, it is of strategic importance to rethink how to teach quantum mechanics both at high school and university levels, keeping in mind also the impact that quantum technologies (quantum networks, quantum computers, …) will have on society. This activity is pursued in collaboration with the group of Physics Education and History of Physics of DIFA.

Collaborations