Landau was first to suggest that collective excitations of particle ensembles could be treated as if they were particles themselves, with properties like momentum and mass. As such, these excitations are known as quasiparticles, and in contrast to free particles they possess a finite lifetime. In this study, we report on the investigation of a particular type of quasiparticle known as a Fermi polaron. This is a quantum impurity that is immersed in a Fermi sea and strongly interacts with it. In particular, Fermi polarons emerging from impurities repelling the surrounding particles are known as repulsive polarons. We could observe well-defined repulsive polarons even at very strong interactions, with impurities possessing the same mass as the surrounding particles. In such a system the existence of long-lived repulsive polarons was thus far debated. For this, we have spectroscopically probed an ultracold Fermi gas of lithium, where atoms in a specific internal spin state acted the role of the impurities interacting with a bath of atoms in another spin state. Our findings offer exciting prospects for studying many-body states that rely on repulsive interactions.

F. Scazza, et al.,
Repulsive Fermi Polarons in a Resonant Mixture of Ultracold ⁶Li Atoms
Phys. Rev. Lett. 118, 083602 (2017)

We demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron ¹⁷³Yb atoms. By mapping the electronic states onto effective sites along a synthetic “electronic” dimension, we have engineered fermionic ladders with synthetic magnetic flux in an experimental configuration that has allowed us to achieve uniform fluxes on a lattice with minimal requirements and unprecedented tunability. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases.

L. F. Livi et al.,
Synthetic Dimensions and Spin-Orbit Coupling with an Optical Clock Transition
Phys. Rev. Lett. 117, 220401 (2016)

We realize a magneto-optical trap for ¹⁶²Dy atoms on the intermediate linewidth transition at 626 nm. We trap over 2✕10⁸ atoms at temperatures as low as 20 μK in 5 seconds. We observe the best loading at large detuning, -35Γ. Under these operating conditions, MOT forms below the quadrupole centre and the MOT light acts as optical pumping as well.

E. Lucioni et al.
A new setup for experiments with ultracold Dysprosium atoms
Eur. Phys. J. Spec. Top. 226, 2775 (2017)

Starting today the Lithium Lab will host the new Marie Sklodowska-Curie project SCOUTFermi2D awarded to Francesco Scazza. Congratulations!

We finished assembling the vacuum setup. In the final cell, we included a passive high finesse optical resonator to transfer a large volume of atoms from the MOT to an optical trap that requires low power.