The Mott insulator is a well know quantum phase appearing in periodic potentials at integer particle fillings. In ordinary matter the potential strength cannot be changed, and it is therefore impossible to study the fate of the Mott insulator for vanishing potential strength. We have now employed an ultracold quantum gas to investigate the superfluid-insulator transition of one-dimensional bosons in shallow periodic potentials. Experimentally, we have performed transport measurements and we have analyzed them with a phase slip based model to accurately determine the Mott transition. We have compared the experimental results with a theoretical analysis based on quantum Monte Carlo simulations in continuum space and Luttinger liquid approach. Experiments and theory are in excellent agreement. Our study provides a quantitative determination of the critical parameters for the Mott transition and defines the regimes of validity of widely used approximate models, namely, the Bose-Hubbard and sine-Gordon models.

G. Boéris et al.
Mott transition for strongly interacting one-dimensional bosons in a shallow periodic potential
Phys. Rev. A 93, 011601(R) (2016)

We report on the experimental observation of a strongly interacting gas of ultracold two-electron fermions with an orbital degree of freedom and magnetically tunable interactions. This realization has been enabled by the demonstration of a novel kind of Feshbach resonance occurring in the scattering of two ¹⁷³Yb atoms in different nuclear and electronic states. The strongly interacting regime at resonance is evidenced by the observation of anisotropic hydrodynamic expansion of the two-orbital Fermi gas. These results pave the way towards the realization of new quantum states of matter with strongly correlated fermions with an orbital degree of freedom.

G. Pagano et al.,
Strongly Interacting Gas of Two-Electron Fermions at an Orbital Feshbach Resonance
Phys. Rev. Lett. 115, 265301 (2015)

See also the Physics Viewpoint by S. Cornish:

S. Cornish
Controlling Collisions in a Two-Electron Atomic Gas
Physics 8, 125 (2015)

In ultracold atoms settings, inelastic light scattering is a preeminent technique to reveal static and dynamic properties at nonzero momentum. In this work, we investigate an array of one-dimensional trapped Bose gases, by measuring both the energy and the momentum imparted to the system via light scattering experiments. The measurements are performed in the weak perturbation regime, where these two quantities — the energy and momentum transferred — are expected to be related to the dynamic structure factor of the system. We discuss this relation, with special attention to the role of in-trap dynamics on the transferred momentum.

N. Fabbri et al.,
Energy and momentum transfer in one-dimensional trapped gases by stimulated light scattering
New J. Phys. 17, 063012 (2015)

Entanglement is a fundamental resource for quantum information processing, occurring naturally in many-body systems at low temperatures. The presence of entanglement and, in particular, its scaling with the size of system partitions underlies the complexity of quantum many-body states. The quantitative estimation of entanglement in many-body systems represents a major challenge, as it requires either full-state tomography, scaling exponentially in the system size, or the assumption of unverified system characteristics such as its Hamiltonian or temperature. Here we adopt recently developed approaches for the determination of rigorous lower entanglement bounds from readily accessible measurements and apply them in an experiment of ultracold interacting bosons in optical lattices of 10⁵ sites. We then study the behaviour of spatial entanglement between the sites when crossing the superfluid-Mott insulator transition and when varying temperature. This constitutes the first rigorous experimental large-scale entanglement quantification in a scalable quantum simulator.

M. Cramer et al.,
Spatial entanglement of bosons in optical lattices
Nat. Commun. 4, 2161 (2013)

We report the Bragg spectroscopy of interacting one-dimensional Bose gases loaded in an optical lattice across the superfluid to the Mott-insulator phase transition. Elementary excitations are created with a nonzero momentum and the response of the correlated 1D gases is in the linear regime. The complexity of the strongly correlated quantum phases is directly displayed in the spectra which exhibit novel features. This work paves the way for a precise characterization of the state of correlated gases in optical lattices.

D. Clément et al.,
Spatial entanglement of bosons in optical lattices
Phys. Rev. Lett. 102, 105301 (2009)

See also the Physics Viewpoint by D. Jaksch:

D. Jaksch
A stimulated atomic response
Physics 2, 29 (2009)