  The phase difference of the macroscopic wave function is a unique structure
of the soliton in an atomic Bose--Einstein condensate (BEC). However,
experiments on ultracold atoms so far have observed the valley of the density
profile to study the dynamics of solitons. We propose a method to observe the
phase difference of a soliton in a BEC by using an interference technique with
Raman and rf pulses. We introduce a phase jump factor, which is an indicator to
measure the phase difference between two points. It is demonstrated by using
the projected Gross--Pitaevskii equation that an interference density ratio,
the density ratio of two-component BECs after the Raman and rf pulses,
reproduces the phase jump factor well. This technique will become an
alternative method to study the decay and breakdown of a phase imprinted
soliton in atomic BECs.
