Theory of a mode-locked atom laser with toroidal geometry

A technique based on the generation of a dark soliton in a ring-shaped Bose-Einstein condensate was considered for mode-locking an atom laser. The soliton has an unexpected property that it has a fractional angular momentum per particle. The dark soliton is created by stirring the condensate at the soliton velocity and cleansed with a periodic out coupler. A synchronized periodic output coupler and gain was used to stabilize the dark soliton to create an atom laser with reproducible coherent waveform. It was shown that the sequence of output pulses were in phase with each other in a mode-locked laser.