Quantum many-body theory

Low-temperature atomic systems manifest phenomena that are strikingly different from classical mechanics. Quantum mechanics implies that energy levels are discrete and this is the foundation of the current definition of the second.

Accuracy and precision of optical clocks are entering a regime where not only single-atom quantum mechanics is crucial, but also quantum many-body phenomena play a relevant role. When going beyond mean-field or perturbative theoretical approaches, their study generically requires massively parallel computation on HPC resources.

We are presently investigating:

the role of ultracold atomic collisions in confined geometries, such as those of optical atomic clocks, to improve their accuracy, by means of quantum Monte Carlo methods;
the dynamics of ultracold atoms in an optical cavity, as a means to generate entanglement for better precision in quantum metrology, by means of computational libraries such as QuTiP, mean-field approaches such as cumulant expansion, and novel time-dependent quantum Monte Carlo methods;
the equation of state of trapped ultracold Fermi and Bose gas mixtures;
the vibrational dynamics of complex molecules

Contact: Gianluca Bertaina

Full list of publications: see here or here

Collaborators:

Stefano Gregorio Giaccari

Available Master theses:

Theoretical and computational study of quantum entangled states in a cavity-enhanced optical clock

In this thesis, the candidate will learn and employ theoretical and computational approaches (alternatively the QuTiP Python libraries, the cumulant expansion or time-dependent variational Monte Carlo) to simulate the quantum dynamics of alkaline-earth atoms in an optical lattice embedded in an optical cavity, with the aim to investigate the best parameters to optimize the generation of non classical states (e.g. spin squeezing) and the reduction of the variance of population measurements.

Quantum Monte Carlo study of interacting cold gases

Cold dilute gases are used for quantum simulation and in optical lattice clocks. Direct interaction between ultracold atoms can be characterized by a few scattering parameters in a partial wave expansion. In spite of the relative simplicity of the theoretical description, the solution of the full many-body Schroedinger equation is a daunting task, that can be efficiently tackled by quantum Monte Carlo simulations. In this thesis, the candidate will develop a quantum Monte Carlo code for the massively parallel computation of the equation of state and structural properties of interacting Fermi or Bose gases in optical traps, possibly investigating their interplay with Rabi coupling to the internal degrees of freedom