We theoretically consider the formation of bright solitons in a mixture of Bose and Fermi degenerate gases. While we assume the forces between atoms in a pure Bose component to be effectively repulsive, their character can be changed from repulsive to attractive in the presence of fermions provided the Bose and Fermi gases attract each other strongly enough. In such a regime the Bose component becomes a gas of effectively attractive atoms. Hence, generating bright solitons in the bosonic gas is possible. Indeed, after a sudden increase of the strength of attraction between bosons and fermions (realized by using a Feshbach resonance technique or by firm radial squeezing of both samples) soliton trains appear in the Bose-Fermi mixture.Solitonic solutions are a very general feature of nonlinear wave equations. Solitons have been studied in many different physical systems ranging from particle physics to optics. They differ from ordinary wave packets as they retain their shape while propagating instead of spreading due to dispersion. This intriguing feature is based on the existence of a nonlinear interaction which compensates for dispersion and produces a self-focusing effect on the propagating wave packet.Dilute atomic quantum gases offer a unique environment to study fundamental solitonic excitations in a pure quantum system with intrinsic nonlinearity. Since the interparticle interaction causing this nonlinearity can be both attractive and repulsive, the Gross-Pitaevskii equation describing the evolution of the condensate wave function exhibits both dark and bright solitonic solutions [1]. Dark solitons as a fundamental excitation in stable BoseEinstein condensates with repulsive interparticle interaction have been studied in different geometries [2,3,4].Bright solitons have been observed in Bose-Einstein condensates of 7 Li in quasi-one-dimensional geometry [5,6]. However, in three-dimensional geometry usually used to prepare the sample the necessary large and negative scattering length leads to density-limited particle numbers (dynamical instability -collapse). The observation of bright solitons was therefore only possible due to magnetic tuning of the interactions from repulsive (used to form a stable Bose-Einstein condensate) to attractive during the experiments.Another experimental approach to bright matter wave solitons was realized in the recently reported observation of gap solitons [7] in a condensate with repulsive interactions by engineering of the matter wave dispersion relation via sophisticated manipulation in a periodic potential (concept of negative effective mass [8]).In this Letter we propose a novel scheme to realize bright solitons in one-dimensional atomic quantum gases. In particular we study the formation of bright solitons in a Bose-Einstein condensate embedded in a quantum degenerate Fermi gas. One important feature is that this mixture allows tuning of the one-dimensional interactions not only by Feshbach resonances but also by simply changing the trap geometry.We consider the bare inte...

The study of cold dilute quantum gases was subject to substantial growth after the experimental realization of Bose-Einstein condensation. Also Fermi systems provide a direct link to condensed matter physics and offer a phase diagram at least as rich as the one for Bose systems. Atomic Fermi quantum gases were recently studied via the observation of quantum degeneracy complemented by first studies on stability and excitations. One of the most intriguing aspects of cold Fermi gases is the Pauli exclusion principle resulting in fundamentally different behaviour compared to bosonic systems. Our experiment goal is to study in detail the restricted excitations in these systems with a particular interest in fermion correlations influenced by the Pauli principle and changed by the presence of bosons or a possible BCS transition.