  We perform large-scale numerical calculations self-consistently solving the
Bogoliubov-de Gennes (BdG) equations in the magnetic field together with random
impurities to directly demonstrate the typical quasi-particle interference
(QPI) in the presence of vortices as observed by scanning tunneling
microscopy/spectroscopy experiments in unconventional superconductors. The
calculations reveal that vortex itself never works as a scatter causing the QPI
pattern but vortex core containing impurity brings about the enhancement of the
sign-preserving QPI peaks. Its origin is Andreev bound-states distorted by
impurity, and all the measurement findings are consistently explained by the
scenario based on the numerical results.
