  The group of real 4 by 4 upper triangular matrices with 1s on the diagonal
has a left-invariant subRiemannian (or Carnot-Caratheodory) structure whose
underlying distribution corresponds to the superdiagonal. We prove that the
associated subRiemannian geodesic flow is not completely integrable. This
provides the first example of a Carnot group (graded nilpotent Lie group with
an invariant subRiemannian structure supported on the generating subspace) with
a non-integrable geodesic flow. We apply this result to prove that the
centralizer for the corresponding quadratic ``quantum'' Hamiltonian in the
universal enveloping algebra for this group is ``as small as possible''.
