New quantum simulations with ultracold Ytterbium gases

In this thesis I report on the experimental results obtained during the years of my PhD in the laboratory of the University of Florence devoted to the investigation of quantum degenerate gases of Ytterbium. I discuss the main results that we achieved, focusing the attention on the experiments concerning two main research lines, the first related to the quantum simulation of synthetic gauge fields with ultracold Yb atoms and the second one to the investigation of two-orbital quantum physics exploiting the 1S0->3P0 clock transition. In particular we have been able to unify these fields of research simulating for the first time a synthetic gauge field for neutral atoms exploiting the orbital degree of freedom offered by two-electron atoms. The realization of artificial gauge fields for neutral atoms is a current trend in the context of quantum simulation and several techniques have been proposed and experimentally realized. Here we adopt a recently proposed quantum simulation scheme which relies on the concept of synthetic dimension. In this scheme an internal degree of freedom of the atom is interpreted as an extra dimension of the system and a hybrid 2D ladder is realized combining this synthetic dimension with a real one-dimensional optical lattice. An artificial magnetic field naturally arises in this hybrid 2D lattice as a consequence of the phase imprinted on the atoms by the laser coupling between the synthetic sites. We exploited this scheme in two different experiments with fermionic 173Yb, in which we map the synthetic dimension in the first case on the ground and clock states of the atom and in the second case on the nuclear spin states of the ground level. Couplings between synthetic sites are realized exploiting single-photon clock transitions and two-photon Raman transitions in the first and second experiment respectively. Despite their simplicity these systems feature some fundamental properties of larger quantum Hall bars, one of which is the presence of chiral currents counter-propagating on the synthetic edges. We have been able to induce and detect these chiral currents in ladders characterized by two and three (only in the Raman case) legs. In the case of the clock approach, for which the experimental realization is simpler, we have also been able to tune the artificial magnetic field and characterized for the first time the strength of the currents as a function of the synthetic flux, a result impossible to achieve in real solid-state systems where magnetic fields of the order of several thousand of Tesla would be required. In the three-leg Raman case we have also investigated the dynamics of the system observing the skipping-orbit-like trajectories performed by fermions in the hybrid space after a quenching of the synthetic tunnelling. In another experiment we used the orbital degree of freedom of 173Yb to demonstrate the possibility to implement Spin-Orbit Coupling (SOC) with single-photon clock transitions in a system of fermionic atoms trapped in a one-dimensional optical lattice, using as pseudospin states the fundamental level 1S0 and the clock state 3P0. This orbital approach to the synthesis of SOC in ultracold gases allows us to overcome some of the limitations imposed by Raman schemes in alkali atoms, where heating due to the presence of intermediate levels has detrimental effects in the observation of many-body processes. The emergence of SOC is detected by evaluating the broadening of the clock spectroscopic response which results from transitions connecting states with different lattice quasimomentum. Our ability to observe these narrow features relies on the high spectroscopic resolution of our clock laser system and is enabled by the long-term stabilization of the laser frequency on the metrological reference delivered by INRiM (the Italian metrological institute) from Turin to Florence through a 642-km-long fiber link. Remarkably, exploiting the long term accuracy provided by the fiber link, we have been able to improve the absolute value of the clock transition in 173Yb by two orders of magnitude with respect to the value previously reported in literature. We exploited the orbital degree of freeedom of 173Yb also to realize a new kind of Feshbach resonance which allows for the tuning of the scattering properties in a mixture of atoms in different orbital states. The possibility to tune interactions by means of standard Feshbach resonances lacked in two-electron atoms due to the absence of a hyperfine structure in the fundamental state. We instead experimentally demonstrated how a similar mechanism is possible also for this class of elements provided that atoms in two different electronic states are considered. In particular, we exploited the orbital Feshbach resonance mechanism to realize a strongly interacting two-orbital gas of 173Yb and characterized the resonance position evaluating the hydrodynamic expansion of the gas. The last part of the thesis reports, instead, some results in which the properties of clock excitation in bosonic 174Yb have been investigated. By means of high resolution spectroscopic measurements on particles confined in 3D optical lattices, the scattering lengths and loss rate coefficients for atoms in different collisional channels involving the ground level 1S0 and the metastable state 3P0 are derived. These quantities, that at our knowledge were still unreported in literature before our work, set important constraints for future experimental studies of two-electron atoms for quantum-technological applications.