Experiments with a Single Bright Matter-Wave Soliton Incident on a Barrier*

The defining property of a soliton is the stability of its shape which arises due to nonlinear self-focusing. We collapse a quasi-1D BEC of $^{7}$Li into a matter-wave soliton containing ${\sim} 60{,}000$ atoms. The collapse is controlled by adiabatically ramping the single-particle scattering length from a large and positive value to slightly negative using the broad magnetic Feshbach resonance in the $| F=1, m_F=1 \rangle$ hyperfine sublevel near 737 G.\footnote{Strecker, K. E., Partridge, G. B., Truscott, A. G. \& Hulet, R. G. Formation and propagation of matter-wave soliton trains. Nature 417, 150-153 (2002).} Dipole oscillations in a weakly harmonic 1D potential are initiated by pulsing on a magnetic field gradient, enabling us to observe the soliton's motion over several oscillation periods. We investigate dynamic interactions of the soliton with a single attractive or repulsive optical defect created by a narrow light sheet at the trap center. A repulsive defect can split a single soliton into two, and on the subsequent interaction at the defect, may enable coherent recombination, thus realizing a matter-wave interferometer.