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No soliton
Dark soliton
Josephson vortex
Subtraction image

Bose-Einstein condensate is coherent quantum matter described by a macroscopic wave function. The wave function includes quantum phase, and hence, interference effects will take place, if different condensates are to overlap. Just as the interference fringe pattern of light from coherent sources can be photographed, the interference fringes of overlapping condensates can be revealed using special imaging techniques. Such interference pattern was obtained experimentally in 1996 for the first time and it is described in Science, 275, 637 (1997). The Bose-Josephson junction considered in this project consists of two parallel atomic waveguides each containing Bose-Einstein condensate. If the confinement of the waveguides is switched off, the Bose-Einstein condensates will expand, overlap and form an interference pattern. This interference pattern will be affected by the presence of a dark soliton or Bose-Josephson vortex in the junction before the expansion. Comparison of different cases is shown in the figures. When no solitons are present in the junction, the interference fringes look similar to the ones obtained in Science, 275, 637 (1997). The presence of a dark soliton or Bose-Josephson vortex produces different patterns. This can be used as a means of their detection and distinction. The last image is showing the difference of intensities between the dark soliton and Bose-Josephson vortex cases. It reveals more details necessary to decide whether originally a dark soliton or a Bose-Josephson vortex was present in the junction. More details can be found in [1]. The images show evolution of expansion from 10 to 50 units of coherence time and the spatial unit on axes is coherence (healing) length.


1. Atomic Josephson vortices , V. M. Kaurov and A. B. Kuklov, Phys. Rev. A 73, 013627 (2006)