Chris Godsil

If A is the adjacency matrix of a graph X, then the matrix exponentialU(t) = exp(itA) determines what physicists term a continuous quantum walk. They ask questions such as: for which graphs are the vertices a and b and a t such that jU(t)a;bj = 1...

If A is the adjacency matrix of a graph X, then the unitary operators defined by U(t) = exp(-itA) define what physicists call a continuous quantum walk. A basic problem is to relate the physical properties of this system to features of the underlying...