Spatiotemporal observation of the soliton-antisoliton collision in a Josephson transmission line

The first experimental observation of a soliton-antisoliton annihilation process in solid state is reported. By precise control of the collision point of a fluxon and an antifluxon in a Josephson transmission line, the annihilation process is observed not only in time but also in space by the Josephson sampler which is coupled to the center of the transmission line. The observed line shapes agree well with the results of numerical calculations which show that a fluxon and an antifluxon fade off in the breather decay mode after collision, and that a fluxon behaves as a relativistic particle.