We report on the experimental characterization of a spatially extended Josephson junction realized with a coherently-coupled two-spin-component Bose-Einstein condensate. The cloud is trapped in an elongated potential such that that transverse spin ex
citations are frozen. We extract the non-linear parameter with three different manipulation protocols. The outcomes are all consistent with a simple local density approximation of the spin hydrodynamics, i.e., of the so-called Bose-Josephson junction equations. We also identify a method to produce states with a well defined uniform magnetization.
Using a multiple-image reconstruction method applied to a harmonically trapped Bose gas, we determine the equation of state of uniform matter across the critical transition point, within the local density approximation. Our experimental results provi
de the canonical description of pressure as a function of the specific volume, emphasizing the dramatic deviations from the ideal Bose gas behavior caused by interactions. They also provide clear evidence for the non-monotonic behavior with temperature of the chemical potential, which is a consequence of superfluidity. The measured thermodynamic quantities are compared to mean-field predictions available for the interacting Bose gas. The limits of applicability of the local density approximation near the critical point are also discussed, focusing on the behavior of the isothermal compressibility.
We experimentally investigate the dynamics of spin solitary waves (magnetic solitons) in a harmonically trapped, binary superfluid mixture. We measure the in-situ density of each pseudospin component and their relative local phase via an interferomet
ric technique we developed, and as such, fully characterise the magnetic solitons while they undergo oscillatory motion in the trap. Magnetic solitons exhibit non-dispersive, dissipationless long-time dynamics. By imprinting multiple magnetic solitons in our ultracold gas sample, we engineer binary collisions between solitons of either same or opposite magnetisation and map out their trajectories.
