One-dimensional Bose gas on an atom chip

We describe experiments investigating the (coherence) properties of a finite-temperature one-dimensional (1D) Bose gas with repulsive interactions. The confining magnetic field is generated with a micro-electronic circuit. This micro-trap for atoms or 'atom chip' is particularly suited to generate a tight waveguide for atoms close to the chip surface. In contrast to the usual case of Bose-Einstein condensation in 3D, in 1D the system is not characterized by long-range phase coherence. Further interest in the 1D Bose gas stems from the fact that it forms the textbook example for the many-body quantum-mechanical systems that can be exactly solved using the Bethe Ansatz. Moreover, using a method developed by Yang and Yang, exact expressions for the thermodynamics of this system can be given. We summarize the theoretical background that is relevant to describe the (nearly) 1D gas in our experiments. The design and construction of our micro-trap is described in some detail. We discuss the technique of Bose-gas focusing, in particular how it applies to our 1D system, and demonstrate that it can be used to probe the momentum distribution of the 1D gas. Finally, we perform a direct comparison of the measured in situ density distribution to the predictions of a model based on the exact Yang-Yang thermodynamics and find very good agreement.