We report on the production of 39 K matter-wave bright solitons, i.e., 1D matter-waves that propagate without dispersion thanks to attractive interactions. The volume of the soliton is studied as a function of the scattering length through three-body losses, revealing peak densities as high as ∼ 5 × 10 20 m −3 . Our solitons, close to the collapse threshold, are strongly bound and will find applications in fundamental physics and atom interferometry.PACS numbers: 03.75. Lm, Solitons are one-dimensional wave-packets that propagate with neither change of shape nor loss of energy. They are a consequence of non-linearities that balance wave-packet spreading due to dispersion. They appear in numerous physical systems such as water waves, optical fibers, plasmas, acoustic waves or even in energy propagation along proteins [1]. Solitons are also observed in ultracold quantum gases [2][3][4][5][6]. In this context, matterwave bright solitons are Bose-Einstein condensates that remain bound thanks to mean-field attractive interactions in a one dimensional geometry [2,3].Matter-wave bright solitons are predicted to be a great tool to locally probe rapidly varying forces for example close to a surface [7,8], or probe (surface) bound states [7,9] which do not appear in linear scattering. For example, the small size of bright solitons has been used in the measurement of quantum reflection from a barrier [10,11]. Because of their dispersion-free propagation, bright solitons are also believed to be good candidates for performing very long time atom interferometry measurements [12] although interactions may cause additional phase shifts [13][14][15][16]. Recently, an experiment demonstrated an increased visibility for a soliton atomic interferometer as compared to its non interacting counterpart [17]. The interactions in solitons can also lead to squeezed or entangled states, which could improve the sensitivity of interferometric measurements beyond the shot noise limit [18][19][20][21][22][23][24]. In some cases, the formation of mesoscopic Schrödinger cat states or NOON states is predicted [25][26][27]. A problem in using these states is losses, such as three-body collisions, which are an intrinsic source of decoherence. They can also induce unusual soliton center of mass dynamics [28].Experiments producing and studying matter-wave bright solitons, despite their interest in both applied and fundamental physics, have remained scarce. In fact, only two elements have been turned into bright solitons, 7 Li [2, 3, 29, 30] and 85 Rb [10,31]. In this paper, we describe the production of 39 K solitons in the |F = 1, m F = −1 state using the Feshbach resonance at 561 G [32] and its associated zero-crossing of the scattering length at 504.4 G (see figure 1). We have optimized the setup in order to produce strongly bound solitons, i.e., solitons with a large negative interaction energy. We thus pro- The evaporation to Bose-Einstein condensation takes place at 550 G (red bullet). The magnetic field is then ramped in two steps to 507 G (vi...

We observe nonlinear scattering of 39 K atomic bright solitons launched in a onedimensional (1D) speckle disorder. We directly compare it with the scattering of non-interacting particles in the same disorder. The atoms in the soliton tend to be collectively either reflected or transmitted, in contrast with the behavior of independent particles in the single scattering regime, thus demonstrating a clear nonlinear effect in scattering. The observed strong fluctuations in the reflected fraction, between zero and 100%, are interpreted as a consequence of the strong sensitivity of the system to the experimental conditions and in particular to the soliton velocity. This behavior is reproduced in a mean-field framework by Gross-Pitaevskii simulations, and mesoscopic quantum superpositions of the soliton being fully reflected and fully transmitted are not expected for our parameters. We discuss the conditions for observing such superpositions, which would find applications in atom interferometry beyond the standard quantum limit.

We study atom losses associated to a previously unreported magnetic Feshbach resonance in potassium 39. This resonance is peculiar in that it presents d-wave character both in the open and in the closed channels, directly coupled by the dominant spin-exchange interaction. The losses associated to a d-wave open-channel resonance present specific signatures such as strong temperature dependance and anisotropic line shapes. The resonance strength and position depend on the axial projection of the orbital angular momentum of the system and are extracted from rigorous multichannel calculations. A two-step model, with an intermediate collision complex being ejected from the trap after collisions with free atoms, permits to reproduce the observed dependance of the loss rate as a function of temperature and magnetic field. PACS numbers: 34.50.Cx, Ultra-cold atoms are many-body quantum systems that offer great control and versatility [1]. Feshbach resonances allow in particular the interatomic interaction to be accurately controlled [2]. Such resonances occur when the kinetic energy of two colliding particles in an open channel becomes close to the energy of a bound state in a closed channel potential. Experimentally, Feshbach resonances in atomic collisions are typically induced and controlled using a variable magnetic field, relying on the different magnetic moment of two free atoms and of the resonant molecular state. The main parameter characterizing the interations at ultra-low temperatures (typically below 1µK), the s-wave scattering length a, can thus be made to vary and accurately controlled. These features have permitted the production of weakly bound molecules for large and positive a [3-8], the study of the BEC-BCS crossover with fermions [10][11][12], and the study of resonantly interacting Bose gases [13][14][15].In the case of spin-exchange interactions between open and closed collision channels, the coupling is isotropic and the orbital angular momentum is conserved. However, other types of coupling such as the dipolar spin-spin interaction are anisotropic and the orbital momentum can change. For example, d-wave or g-wave resonances, where d and g refer to the symmetry of the bound state have been reported for collisions in the s-wave [2,16,17]. Higher partial wave collisions in the entrance channel can also become resonant at higher energies. These resonances then have specific features and signatures as the collision rates strongly depends on the collision energy due to the centrifugal barrier that needs to be overcome. Feshbach resonances with higher partial waves in the entrance channel have been reported in p-waves [18-20] and also in d-waves [21-23]. A d-wave shape resonance was also discovered in 41 K [24]. Close to these resonances for fermions, high-order-wave pairing is expected, while p-wave and d-wave pairing plays a key role in superfluid liquid 3 He [25] or in d-wave Hi-Tc superconductors [26].For bosons, molecular condensates of rotating molecules are predicted [27]. Progresses in these direc...