We investigate the behavior of a weakly interacting nearly one-dimensional (1D) trapped Bose gas at finite temperature. We perform in situ measurements of spatial density profiles and show that they are very well described by a model based on exact solutions obtained using the Yang-Yang thermodynamic formalism, in a regime where other, approximate theoretical approaches fail. We use Bose-gas focusing [Shvarchuck et al., Phys. Rev. Lett. 89, 270404 (2002)] to probe the axial momentum distribution of the gas, and find good agreement with the in situ results.PACS numbers: 03.75. Hh, 05.30.Jp, 05.70.Ce Reducing the dimensionality in a quantum system can have dramatic consequences. For example, the 1D Bose gas with repulsive delta-function interaction exhibits a surprisingly rich variety of physical regimes that is not present in 2D or 3D [1,2]. This 1D Bose gas model is of particular interest because exact solutions for the manybody eigenstates can be obtained using a Bethe ansatz [3]. Furthermore, the finite-temperature equilibrium can be studied using the Yang-Yang thermodynamic formalism [4,5,6], a method also known as the thermodynamic Bethe ansatz. This formalism is the unifying framework for the thermodynamics of a wide range of exactly solvable models. It yields solutions to a number of important interacting many-body quantum systems and as such provides critical benchmarks to condensed-matter physics and field theory [6]. The specific case of the 1D Bose gas as originally solved by Yang and Yang [4] is of particular interest because it is the simplest example of the formalism. The experimental achievement of ultracold atomic Bose gases in the 1D regime [7] has attracted renewed attention to the 1D Bose gas problem [8] and is now providing previously unattainable opportunities to test the Yang-Yang thermodynamics.In this paper, we present the first direct comparison between experiments and theory based on the Yang-Yang exact solutions. The comparison is done in the weakly interacting regime and covers a wide parameter range where conventional models fail to quantitatively describe in situ measured spatial density profiles. Furthermore, we use Bose-gas focusing [9] to probe the equilibrium momentum distribution of the 1D gas, which is difficult to obtain through other means.For a uniform 1D Bose gas, the key parameter is the dimensionless interaction strength γ = mg/ 2 n, where m is the mass of the particles, n is the 1D density, and g is the 1D coupling constant. At low densities or large coupling strength such that γ ≫ 1, the gas is in the strongly interacting or Tonks-Girardeau regime [10]. The opposite limit γ ≪ 1 corresponds to the weakly interacting gas. Here, for temperatures below the degeneracy temperature T d = 2 n 2 /2mk B , one distinguishes two regimes [11]. (i) For sufficiently low temperatures, T ≪ √ γT d , the equilibrium state is a quasi-condensate with suppressed density fluctuations. The system can be treated by the mean-field approach and by the Bogoliubov theory of excitations. The 1D c...

We present the implementation of tailored trapping potentials for ultracold gases on an atom chip. We realize highly elongated traps with box-like confinement along the long, axial direction combined with conventional harmonic confinement along the two radial directions. The design, fabrication and characterization of the atom chip and the box traps is described. We load ultracold ( 1 µK) clouds of 87 Rb in a box trap, and demonstrate Bose-gas focusing as a means to characterize these atomic clouds in arbitrarily shaped potentials. Our results show that box-like axial potentials on atom chips are very promising for studies of one-dimensional quantum gases.

Experiments on ultracold gases offer unparalleled opportunities to explore quantum manybody physics, with excellent control over key parameters including temperature, density, interactions and even dimensionality. In some systems, atomic interactions can be adjusted by means of magnetic Feshbach resonances, which have played a crucial role in realizing new many-body phenomena. However, suitable Feshbach resonances are not always available, and they offer limited freedom since the magnetic field strength is the only control parameter. Here we show a new way to tune interactions in one-dimensional quantum gases using state-dependent dressed potentials, enabling control over non-equilibrium spin motion in a two-component gas of 87 Rb. The accessible range includes the point of spinindependent interactions where exact quantum many-body solutions are available and the point where spin motion is frozen. This versatility opens a new route to experiments on spin waves, spin-"charge" separation and the relation between superfluidity and magnetism in low-dimensional quantum gases.Advances in optical and magnetic trapping of ultracold gases have played an essential role in opening up novel avenues in quantum many-body physics by providing experimental access to new physical regimes [1]. In particular, one-dimensional (1D) quantum gases, created using optical lattices or atom chips, exhibit a surprisingly rich variety of regimes not present in 2D or 3D [2][3][4][5][6][7][8][9]. For example, a 1D Bose gas becomes more strongly interacting as the density decreases.Furthermore, the many-body eigenstates and thermodynamic properties of these 1D systems can often be described using exact Bethe Ansatz methods [10-14], and direct comparisons between theory and experiment are possible [6,8,9,[15][16][17]. Adding the possibility to dynamically control the strength of atomic interactions, for example via Feshbach resonances [16,[18][19][20], there is now a strong impetus to extend these experimental and theoretical studies to non-equilibrium dynamics.Spinor quantum gases offer the opportunity to study the interplay between internal (spin) and external (motion) degrees of freedom [16,17,[21][22][23][24][25][26][27]. In this context, strong candidates for experiments are the two magnetically trappable clock states in 87 Rb [23,25], in part because they experience equal trapping potentials and have nearly spin-independent interactions [28][29][30].The drawback is that no convenient Feshbach resonances are available for these states, preventing

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Abstract. We describe the realization of atom-optical elements as magnetic waveguide potentials, beam splitters and gravitational traps on a microchip. The microchip was produced by electroplating gold conductors on an aluminiumoxide substrate. The conductors are 30-150 µm wide and allow for the generation of waveguides at large distances to the chip surface, where surface effects are negligible. We show that these elements can be integrated on a single chip to achieve complex atom-optical circuits. PACS