Pretty Good State Transfer on Circulant Graphs

Let G be a graph with adjacency matrix A. The transition matrix of G relative to A is defined by H(t) := exp (−itA), where t ∈ R. The graph G is said to admit pretty good state transfer between a pair of vertices u and v if there exists a sequence of real numbers {tk} and a complex number γ of unit modulus such that lim k→∞ H(tk)eu = γev. We find that the cycle Cn as well as its complement Cn admit pretty good state transfer if and only if n is a power of two, and it occurs between every pair of antipodal vertices. In addition, we look for pretty good state transfer in more general circulant graphs. We prove that union (edge disjoint) of an integral circulant graph with a cycle, each on 2k (k > 3) vertices, admits pretty good state transfer. The complement of such union also admits pretty good state transfer. Using Cartesian products, we find some non-circulant graphs admitting pretty good state transfer.