J. Catani

Direct Observation of Coherent Interorbital Spin-Exchange Dynamics

We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold 173Yb fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of 173Yb atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism.

Observation of chiral edge states with neutral fermions in synthetic Hall ribbons

Visualizing edge states in atomic systems Visualizing edge states in atomic systems Simulating the solid state using ultracold atoms is an appealing research approach. In solids, however, the charged electrons are susceptible to an external magnetic field, which curves their trajectories and makes them skip along the edge of the sample. To observe this phenomenon with cold atoms requires an artificial magnetic field to have a similar effect on the neutral atoms (see the Perspective by Celi and Tarruell). Stuhl et al. obtained skipping orbits with bosonic atoms using a lattice that consisted of an array of atoms in one direction and three internal atomic spin states in the other. In a complementary experiment, Mancini et al. observed similar physics with fermionic atoms. Science, this issue pp. 1514 and 1510; see also p. 1450 Analogs of quantum-Hall-effect edge states are observed with fermionic ytterbium-173 atoms in a synthetic lattice. [Also see Perspective by Celi and Tarruell] Chiral edge states are a hallmark of quantum Hall physics. In electronic systems, they appear as a macroscopic consequence of the cyclotron orbits induced by a magnetic field, which are naturally truncated at the physical boundary of the sample. Here we report on the experimental realization of chiral edge states in a ribbon geometry with an ultracold gas of neutral fermions subjected to an artificial gauge field. By imaging individual sites along a synthetic dimension, encoded in the nuclear spin of the atoms, we detect the existence of the edge states and observe the edge-cyclotron orbits induced during quench dynamics. The realization of fermionic chiral edge states opens the door for edge state interferometry and the study of non-Abelian anyons in atomic systems.

Double Species Bose-Einstein Condensate with Tunable Interspecies Interactions

We produce Bose-Einstein condensates of two different species, 87Rb and 41K, in an optical dipole trap in proximity of interspecies Feshbach resonances. We discover and characterize two Feshbach resonances, located around 35 and 79 G, by observing the three-body losses and the elastic cross section. The narrower resonance is exploited to create a double species condensate with tunable interactions. Our system opens the way to the exploration of double species Mott insulators and, more in general, of the quantum phase diagram of the two-species Bose-Hubbard model.

A one-dimensional liquid of Fermions with tunable spin

The physics of one-dimensional many-body systems is rich but still insufficiently understood. An ultracold atom experiment investigates the behaviour of one-dimensional strongly correlated fermions with a tunable number of spin components.

39K Bose-Einstein condensate with tunable interactions.

We produce a Bose-Einstein condensate of 39K atoms. Condensation of this species with a naturally small and negative scattering length is achieved by a combination of sympathetic cooling with 87Rb and direct evaporation, exploiting the magnetic tuning of both inter- and intraspecies interactions at Feshbach resonances. We explore the tunability of the self-interactions by studying the expansion and the stability of the condensate. We find that a 39K condensate is interesting for future experiments requiring a weakly-interacting Bose gas.

Observation of Heteronuclear Atomic Efimov Resonances

Building on the recent experimental observation with ultracold atoms, we report the first experimental evidence of Efimov physics in a heteronuclear system. A mixture of ;{41}K and ;{87}Rb atoms was cooled to few hundred nanokelvins and stored in an optical dipole trap. Exploiting a broad interspecies Feshbach resonance, the losses due to three-body collisions were studied as a function of the interspecies scattering length. We observe an enhancement of the three-body collisions for three distinct values of the interspecies scattering lengths, both positive and negative, where no Feshbach resonances are expected. We attribute the two features at negative scattering length to the existence of two kinds of Efimov trimers, KKRb and KRbRb.

Degenerate Bose-Bose mixture in a three-dimensional optical lattice

Quantum degenerate gases are formidable systems to shine light on fundamental quantum phenomena occurring at extremely low temperatures, such as superconductivity and superfluidity. In combination with optical lattices and scattering resonances, degenerate gases give rise to strongly correlated systems, enriching even further the breadth of phenomena that can be directly probed. Indeed, the pioneering experiment on the superfluid to Mott-insulator transition [1] has shown how physical models long studied in the field of condensed matter can be realized almost ideally. With two different atomic species, the wealth of quantum phases grows to a daunting complexity [2], only marginally explored by experiments. Actually, experiments with heteronuclear mixtures in three-dimensional (3D) optical lattice have been performed very recently only for Fermi-Bose systems [3, 4], while Fermi-Fermi and Bose-Bose mixtures are yet uncharted territory. The importance of mixtures in optical lattices is hardly overstated: association of dipolar molecules [5], mapping of spin arrays [6], schemes for quantum calculation [7], and implementation of disorder [8] represent only a few major research lines that potentially will greatly benefit from such systems. In particular, Bose-Bose mixtures seem well suited for all these purposes, provided that collisional losses are adequately suppressed. This work reports the first realization of a degenerate Bose-Bose heteronuclear mixture in a 3D optical lattice. Exploiting the large mass difference, we investigate the regime where one species lies well in the superfluid domain, while the other exhibits the disappearence of the interference pattern usually associated with the transition from a superfluid to a Mott insulator. We focus only

Entropy Exchange in a Mixture of Ultracold Atoms

We investigate experimentally the entropy transfer between two distinguishable atomic quantum gases at ultralow temperatures. Exploiting a species-selective trapping potential, we are able to control the entropy of one target gas in presence of a second auxiliary gas. With this method, we drive the target gas into the degenerate regime in conditions of controlled temperature by transferring entropy to the auxiliary gas. We envision that our method could be useful both to achieve the low entropies required to realize new quantum phases and to measure the temperature of atoms in deep optical lattices. We verified the thermalization of the two species in a 1D lattice.

Scattering in mixed dimensions with ultracold gases.

We experimentally investigate the mix-dimensional scattering occurring when the collisional partners live in different dimensions. We employ a binary mixture of ultracold atoms and exploit a species-selective 1D optical lattice to confine only one atomic species in 2D. By applying an external magnetic field in proximity of a Feshbach resonance, we adjust the free-space scattering length to observe a series of resonances in mixed dimensions. By monitoring 3-body inelastic losses, we measure the magnetic field values corresponding to the mix-dimensional scattering resonances and find a good agreement with the theoretical predictions based on simple energy considerations.

Optically induced lensing effect on a Bose-Einstein condensate expanding in a moving lattice

We report the experimental observation of a lensing effect on a Bose-Einstein condensate expanding in a moving 1D optical lattice. The effect of the periodic potential can be described by an effective mass dependent on the condensate quasimomentum. By changing the velocity of the atoms in the frame of the optical lattice, we induce a focusing of the condensate along the lattice direction. The experimental results are compared with the numerical predictions of an effective 1D theoretical model. In addition, a precise band spectroscopy of the system is carried out by looking at the real-space propagation of the atomic wave packet in the optical lattice.