Superconductivity and superfluidity of fermionic and bosonic systems are remarkable many--body quantum phenomena. In liquid helium and dilute gases, Bose and Fermi superfluidity has been observed separately, but producing a mixture in which both the fermionic and the bosonic components are superfluid is challenging. Here we report on the observation of such a mixture with dilute gases of two Lithium isotopes, 6 Li and 7 Li. We probe the collective dynamics of this system by exciting center--of--mass oscillations that exhibit extremely low damping below a certain critical velocity. Using high precision spectroscopy of these modes we observe coherent energy exchange and measure the coupling between the two superfluids. Our observations can be captured theoretically using a sum--rule approach that we interpret in terms of two coupled oscillators.In recent years, ultracold atoms have emerged as a unique tool to engineer and study quantum many--body systems. Examples include weakly interacting Bose--Einstein condensates [1,2], two--dimensional gases [3], and the superfluid--Mott insulator transition [4] in the case of bosonic atoms, and the crossover between Bose--Einstein condensation (BEC) and fermionic superfluidity described by Bardeen, Cooper and Schrieffer's theory (BCS) for fermionic atoms Bose gas is sympathetically driven to quantum degeneracy.The two clouds reach the superfluid regime after a 4--second evaporation ramp [10]. As the 7 Li Bose gas is weakly interacting, the onset of BEC is detected by the growth of a narrow peak in the density profile of the cloud. From previous studies on atomic Bose--Einstein condensates, we conclude that the 7 Li BEC is in a superfluid phase. Superfluidity in a unitaryFermi gas is notoriously more difficult to detect because of the absence of any qualitative modification of the density profile at the phase transition. To demonstrate the superfluidity of the fermionic component of the cloud, we slightly imbalance the two spin populations. In an imbalanced gas, the cloud is organized in concentric layers, with a fully paired superfluid region at its center where Cooper pairing maintains equal spin populations. This 6 Li superfluid core can be detected by the presence of a plateau in the doubly integrated density difference [12].Examples of density profiles of the bosonic and fermionic superfluids are shown in Fig is the geometric mean trapping frequency for 7 Li ( 6 Li). Combined with the observation of the 6 Li plateau, this implies that the Fermi cloud is also superfluid with a temperature below 0.8 !,! .Here !,! is the critical temperature for superfluidity of a spin--balanced, harmonically trapped Fermi gas at unitarity,The superfluid mixture is very stable with a lifetime exceeding 7s for our coldest samples.As seen in Fig. 1, the Bose--Fermi interaction is too weak to alter significantly the density profiles of the two species [14]. To probe the interaction between the two superfluids we study the dynamics of the mass centers of the two isotopes (dipole modes), a schem...

We study cold collisions between trapped ions and trapped atoms in the semiclassical (Langevin) regime. Using Yb+ ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes over three decades of collision energies down to 3 mueV (k_{B}x35 mK). The minimum measured rate coefficient of 6x10;{-10} cm;{3} s;{-1} is in good agreement with that derived from a Langevin model for an atomic polarizability of 143 a.u.