  Constrained quantum annealing (CQA) is a quantum annealing approach that is
designed so that constraints are satisfied without penalty terms. There is an
analogy between the model for the CQA of graph coloring and a set of disordered
spin chains. In the model for the CQA of graph coloring, disorder corresponds
to the fluctuation of effective local fields that increase in a CQA process.
Numerical simulations of effective fields and entanglement demonstrate how
localization appears in the CQA. Some notable features appear in the
concurrence, which is a measure of entanglement, plotted as a function of the
fluctuation of effective fields.
