A closed-trajectory evolution of a quantum state generally imprints a phase that contains both dynamical and geometrical contributions. While dynamical phases depend on the reference system, geometric phase factors are uniquely defined by the properties of the outlined trajectory. Here, we generate and measure geometric phases in a Bose-Einstein condensate of ⁸⁷Rb using a combination of dynamical quantum Zeno effect and measurement-free evolution. We show that the dynamical quantum Zeno effect can inhibit the formation of a geometric phase without altering the dynamical phase. This can be used to extract the geometric Aharonov-Anandan phase from any closed-trajectory evolution without requiring knowledge or control of the Hamiltonian.

H.–V. Do et al.,
Measuring geometric phases with a dynamical quantum Zeno effect in a Bose-Einstein condensate
Phys. Rev. Research 1, 033028 (2019)

We report on the study of binary collisions between quantum droplets formed by an attractive mixture of ultracold atoms. We distinguish two main outcomes of the collision, i.e., merging and separation, depending on the velocity of the colliding pair. The critical velocity v_c that discriminates between the two cases displays a different dependence on the atom number N for small and large droplets. By comparing our experimental results with numerical simulations, we show that the nonmonotonic behavior of v_c is due to the crossover from a compressible to an incompressible regime, where the collisional dynamics is governed by different energy scales, i.e., the droplet binding energy and the surface tension. These results also provide the first evidence of the liquidlike nature of quantum droplets in the large N limit, where their behavior closely resembles that of classical liquid droplets.

G. Ferioli et al.,
Collisions of Self-Bound Quantum Droplets
Phys. Rev. Lett. 122, 090401 (2019)

Lorenzo Francesco Livi has been awarded with a prize from Florence University Press for the best PhD thesis discussed in 2018 at University of Florence among all the scientific disciplines. The prize will consist in the publication of the thesis, titled "New quantum simulations with ultracold Ytterbium gases", by Florence University Press. The diploma has been given to Lorenzo by Prof. Luigi Dei, Rector of the University of Florence, in a public ceremony. Congratulations!

Lorenzo Francesco Livi
New quantum simulations with ultracold Ytterbium gases
PhD thesis - University of Firenze (2018)

The competition of dipole-dipole and contact interactions leads to exciting new physics in dipolar gases, well-illustrated by the recent observation of quantum droplets and rotons in dipolar condensates. We have now discovered that the combination of the roton instability and quantum stabilization leads under proper conditions to a novel regime that presents supersolid properties, due to the coexistence of periodic density modulation and phase coherence. In a combined experimental and theoretical analysis (with the University of Hannover), we have determined the parameter regime for the formation of coherent stripes, whose lifetime of a few tens of milliseconds is limited by the eventual destruction of the stripe pattern due to three-body losses. Our results open intriguing prospects for the development of long-lived dipolar supersolids.

L. Tanzi et al.
Observation of a dipolar quantum gas with metastable supersolid properties
Phys. Rev. Lett. 122, 130405 (2019)

See also the reviews on Physics Viewpoint by T. Donner:

T. Donner, Dipolar Quantum Gases go Supersolid
Physics 12, 38 (2019)
also featured in Highlights of the Year, Physics 12, 145 (2019)

and the Nature News and Views by L. Pollet:

L. Pollet, Quantum gases show flashes of a supersolid
Nature 569, 494 (2019)

Ultracold molecules have experienced increasing attention in recent years. Compared to ultracold atoms, they possess several unique properties that make them perfect candidates for the implementation of new quantum-technological applications in several fields, from quantum simulation to quantum sensing and metrology. In particular, ultracold molecules of two-electron atoms (such as strontium or ytterbium) also inherit the peculiar properties of these atomic species, above all, the possibility to access metastable electronic states via direct excitation on optical clock transitions with ultimate sensitivity and accuracy. We report on the production and coherent manipulation of molecular bound states of two fermionic ¹⁷³Yb atoms in different electronic (orbital) states ¹S₀ and ^eP₀ in the proximity of a scattering resonance involving atoms in different spin and electronic states, called orbital Feshbach resonance. We demonstrate that orbital molecules can be coherently photoassociated starting from a gas of ground-state atoms in a three-dimensional optical lattice by observing several photoassociation and photodissociation cycles. We also show the possibility to coherently control the molecular internal state by using Raman-assisted transfer to swap the nuclear spin of one of the atoms forming the molecule, thus demonstrating a powerful manipulation and detection tool of these molecular bound states. Finally, by exploiting this peculiar detection technique we provide the first information on the lifetime of the molecular states in a many-body setting, paving the way towards future investigations of strongly interacting Fermi gases in a still unexplored regime.

G. Cappellini, et al.
Coherent Manipulation of Orbital Feshbach Molecules of Two-Electron Atoms
Phys. Rev. X 9, 011028 (2019)