Discrete Quantum Walks with Marked Vertices and Their Average Vertex Mixing Matrices

We study the discrete quantum walk that assigns negative identity coins to marked vertices and Grover coins to the unmarked ones. We find combinatorial bases for the eigenspaces of the transtion matrix, and derive a formula for the average vertex mixing matrix. We then explore properties of this matrix when the marked vertices or unmarked vertices are neighborhood-equitable in the vertex-deleted subgraph.