  Since constraints hinder the application of numerical algorithms, phase
diagrams of quantum dimer models are still controversial, even on the square
lattice. The core controversy is whether the mixed state exists. In this
article, we give strong evidences to solve this dispute. With our newly
developed sweeping cluster method, we studied the phase diagram of large
parameter space by introducing the definition of pair correlation function and
other supporting evidence to distinguish the mixed phase from the columnar
phase with high precision. In particular, we find that the ground state
corresponds to the mixed phase for a vast parameter region.
