Dark solitons in cigar-shaped Bose-Einstein condensates of 87 Rb are created by a phase imprinting method. Coherent and dissipative dynamics of the solitons has been observed.

Solitons are among the most distinguishing fundamental excitations in a wide range of non-linear systems such as water in narrow channels, high speed optical communication, molecular biology and astrophysics. Stabilized by a balance between spreading and focusing, solitons are wavepackets, which share some exceptional generic features like form-stability and particle-like properties. Ultracold quantum gases represent very pure and well-controlled non-linear systems, therefore offering unique possibilities to study soliton dynamics. Here we report on the first observation of long-lived dark and dark-bright solitons with lifetimes of up to several seconds as well as their dynamics in highly stable optically trapped 87 Rb Bose-Einstein condensates. In particular, our detailed studies of dark and dark-bright soliton oscillations reveal the particle-like nature of these collective excitations for the first time. In addition, we discuss the collision between these two types of solitary excitations in Bose-Einstein condensates. The dynamics of non-linear systems plays an essential role in nature, ranging from strong non-linear interactions of elementary particles to non-linear wave phenomena in oceanography and meteorology. A special class of non-linear phenomena are solitons with interesting particle and wave-like behaviour. Reaching back to the observation of "waves of translation" in a narrow water channel by Scott-Russell in 1834 [1], solitons are nowadays recognized to appear in various systems as different as astrophysics, molecular biology and non-linear optics [2]. They are characterized as localized solitary wavepackets that maintain their shape and amplitude caused by a self-stabilization against dispersion via a non-linear interaction. While an early theoretical explanation of this non-dispersive wave phenomenon was given by Korteweg and de Vries in the late 19th century it was not before 1965 that numerical simulations of Zabusky and Kruskal theoretically proved that these solitary waves preserve their identity in collisions [3,4]. This revelation led to the term "soliton" for this type of collective excitation. Nowadays solitons are a very active field of research in many areas of science. In the field of non-linear optics they attract enormous attention due to applications in fast data transfer. Bose-Einstein condensates (BEC) of weakly interacting atoms offer fascinating possibilities for the study of nonlinear phenomena, as they are very pure samples of ultracold gases building up an effective macroscopic wave function of up to mm size. Non-linear effects like collective excitations [5], four-wave mixing [6] and vortices [7,8] have been studied, to name only a few examples. The existence and some fundamental properties of solitons have been deduced from few experiments employing ultra-cold quantum gases. Bright solitons, characterized as non-spreading matter-wave packets, have been observed in BEC with attractive interaction [9,10,11] where they represent the ground state of the system. In a repulsively...

We observe a localized phase of ultracold bosonic quantum gases in a 3-dimensional optical lattice induced by a small contribution of fermionic atoms acting as impurities in a Fermi-Bose quantum gas mixture. In particular, we study the dependence of this transition on the fermionic (40)K impurity concentration by a comparison to the corresponding superfluid to Mott-insulator transition in a pure bosonic (87)Rb gas and find a significant shift in the transition parameter. The observed shift is larger than expected based on a simple mean-field argument, which indicates that disorder-related effects play a significant role.

We report on the creation of ultracold heteronuclear molecules assembled from fermionic 40 K and bosonic 87 Rb atoms in a 3D optical lattice. Molecules are produced at a heteronuclear Feshbach resonance both on the attractive and the repulsive side of the resonance. We precisely determine the binding energy of the heteronuclear molecules from rf spectroscopy across the Feshbach resonance. We characterize the lifetime of the molecular sample as a function of magnetic field and measure between 20 and 120ms. The efficiency of molecule creation via rf association is measured and is found to decrease as expected for more deeply bound molecules.PACS numbers: 03.75. Kk, 03.75.Ss, 32.80.Pj, 34.20.Cf, There has been a long quest for production of ultracold molecules in recent years. In particular, heteronuclear molecules would open up intriguing perspectives both in view of their internal properties and their interactions. The electric dipole moment of heteronuclear molecules in their internal ground states makes them one of the best candidates for tests of fundamental physics like the search for a permanent electric dipole moment of the electron and parity violation [1] as well as for studies on the drifts of fundamental constants. In addition, polar molecules are a key for novel promising quantum computation schemes [2]. Furthermore, their large anisotropic interactions give rise to quantum magnetism [3], new types of superfluid pairing [4] and a variety of quantum phases [5]. Currently, two main routes to the production of ultracold molecules are being pursued. One approach aims at cooling thermal ensembles of molecules, e. g. using buffer gas cooling [6], Stark deceleration [7] or velocity filtering [8]. The other approach starts with ultracold atomic ensembles and assembles them into molecules by means of photoassociation [9] or Feshbach resonances [10]. In the latter case, one major issue has been the stability of these molecules. While molecules created in bosonic quantum gases have a very short collisional lifetime, bosonic molecules from two fermionic atoms are relatively stable due to the Pauli principle [11]. In other cases, as recently demonstrated for bosonic samples [12] and also expected for heteronuclear mixtures, it is favorable to produce the molecules in separated wells of optical lattices to suppress collisional inelastic losses. So far, molecules produced at Feshbach resonances have been limited to homonuclear systems.In this letter we report on the first creation of ultracold heteronuclear molecules in a 3D optical lattice at a Feshbach resonance. This approach produces ultracold molecules in the ground state of individual lattice sites. This method offers several advantages: long lifetimes allow for further manipulation towards the internal molecular ground state. Moreover, the inherent order within the lattice enables studies of new quantum phases of dipoledipole interacting systems. In particular, we perform rf association of fermionic 40 K and bosonic 87 Rb atoms close to a heteronuclear Feshba...

Atom interferometers covering macroscopic domains of space-time are a spectacular manifestation of the wave nature of matter. Because of their unique coherence properties, Bose-Einstein condensates are ideal sources for an atom interferometer in extended free fall. In this Letter we report on the realization of an asymmetric Mach-Zehnder interferometer operated with a Bose-Einstein condensate in microgravity. The resulting interference pattern is similar to the one in the far field of a double slit and shows a linear scaling with the time the wave packets expand. We employ delta-kick cooling in order to enhance the signal and extend our atom interferometer. Our experiments demonstrate the high potential of interferometers operated with quantum gases for probing the fundamental concepts of quantum mechanics and general relativity.