  We use quantum sine-Gordon model to describe the low energy dynamics of a
pair of coupled one-dimensional condensates of interacting atoms. We show that
the nontrivial excitation spectrum of the quantum sine-Gordon model, which
includes soliton and breather excitations, can be observed in experiments with
time-dependent modulation of the tunneling amplitude, potential difference
between condensates, or phase of tunneling amplitude. We use the form-factor
approach to compute structure factors corresponding to all three types of
perturbations.
