 Before looking at these questions, there is the thorny problem of defining quantum chaos. The difficulties in establishing an agreed definition of quantum chaos are actually more challenging than for classical chaos (§1). Recall that there were several subtleties involved in attempting to arrive at a consensus definition of classical chaos. One important proposal for a necessary condition is the presence of some form of stretching and folding mechanism associated with a nonlinearity in the system. However, since Schrödinger’s equation is linear, quantum mechanics is a linear theory. This means that quantum states starting out initially close remain just as close (in Hilbert space norm) throughout their evolution. So in contrast to chaos in classical physics, there is no separation (exponential or otherwise) between quantum states under Schrödinger evolution. The best candidates for a necessary condition for chaos appear to be missing from the quantum domain. 