We report the experimental realization of a new kind of optical lattice for ultra-cold atoms where arbitrarily large separation between the sites can be achieved without renouncing to the stability of ordinary lattices. Two collinear lasers, with slightly different commensurate wavelengths and retrorefected on a mirror, generate a superlattice potential with a periodic \beat-note" profile where the regions with large amplitude modulation provide the effective potential minima for the atoms. To prove the analogy with a standard large spacing optical lattice we study Bloch oscillations of a Bose Einstein condensate with negligible interactions in the presence of a small force. The observed dynamics between sites separated by ten microns for times exceeding one second proves the high stability of the potential. This novel lattice is the ideal candidate for the coherent manipulation of atomic samples at large spatial separations and might find direct application in atom-based technologies like trapped atom interferometers and quantum simulators.

L. Masi, et al.,
Spatial Bloch Oscillations of a Quantum Gas in a “Beat-Note” Superlattice
Phys. Rev. Lett. 127, 020601 (2021)

We report on our patented Littrow-type external cavity diode laser (ECDL) in which the coarse wavelength adjustment obtained via the rotation of a diffraction grating is decoupled from the fine tuning of the cavity modes done with changes in the external cavity length. This design improves the robustness of the ECDL emission against misalignment and hysteresis, even for the case of long external cavity lasers typically employed in optical clock experiments.

L. Duca, et al.
Design of a Littrow-type diode laser with independent control of cavity length and grating rotation
Opt. Lett. 46, 2840 (2021)

A key manifestation of superfluidity in liquids and gases is a reduction of the moment of inertia under slow rotations. Non-classical rotational effects have been searched for a long time also for the elusive supersolid phase of matter, in which superfluidity coexists with a lattice structure. Here we show that the recently discovered supersolid phase in dipolar quantum gases features a reduced moment of inertia. We study a peculiar rotational oscillation mode in a harmonic potential, the scissors mode, already employed for superfluids. From the measured moment of inertia, we derive a superfluid fraction in analogy with the original definition by A. J. Leggett. The superfluid fraction is different from zero and of order of unity, providing direct evidence of the superfluid nature of the dipolar supersolid. A qualitative comparison with the original theoretical model supports the observation of a large superfluid fraction close to the transition from the Bose-Einstein condensate (BEC) and the supersolid.

L. Tanzi, et al.
Evidence of superfluidity in a dipolar supersolid from non-classical rotational inertia
Science 371, 1162 (2021)

By investigating the tunneling transport of ultracold atomic Fermi gases, we reveal for the first time a peculiar enhancement of the conductance of neutral superfluids, in contrast with charged superconductors. — Both superfluids and superconductors owe their distinctive frictionless flow to their condensed nature, namely the macroscopic occupation of a single quantum state. Regardless of the electric charge of the constituent particles, condensation results in the emergence of the Josephson effect: a tunneling current flows when two superfluid reservoirs are coupled with one another through a thin insulating barrier in a so-called Josephson junction.
Exactly as their superconducting counterparts, fermionic superfluids composed of ultracold atoms can support the flow of a dissipationless current through the junction up to a maximum value. This maximum Josephson current is directly connected to the condensate density, as we demonstrated in a previous study in the low-temperature limit, and extended in this work to finite temperatures across the superfluid transition.
For higher currents instead, the junction behaves resistively, giving rise to a finite Ohmic conductance, which we find to massively exceed the value observed in charged electronic junctions. Such large anomalous conductance, fostered by the condensate coupling with sound wave excitations, is tightly linked to charge neutrality boosting particle transport through the junction. This behavior is indeed absent in electronic junctions, where Coulomb interactions inhibit sound waves and the conductance is essentially given by the tunneling of non-condensed particles.

G. Del Pace et al.
Tunneling Transport of Unitary Fermions across the Superfluid Transition
Phys. Rev. Lett. 126, 055301 (2021)

It is a great privilege for us to welcome Nigel Cooper, Professor in Theoretical Physics of University of Cambridge. Prof. Cooper will honour us with his presence for one year as a Visiting Professor of the Department of Physics and Astronomy of the University of Florence.
The research interests of Prof. Cooper are focused on the nature and properties of the novel phases of matter that can emerge as a result of quantum mechanical effects in interacting many-particle systems. In particular, he is a world leader in the investigation of the role of topology in the collective properties of ultra-cold atomic gases and of the electronic properties of novel solid state materials. He was awarded the 2007 Maxwell Medal and Prize by the Institute of Physics, a Humboldt Research Award (2013), an EPSRC Established Career Fellowship (2013), a Simons Investigator Award (2017) and the 2019 Lord Rayleigh Prize of the IOP.