  The orientation in space of a Cartesian coordinate system can be indicated by
the two vectorial constants of motion of a classical Keplerian orbit: the
angular momentum and the Laplace-Runge-Lenz vector. In quantum mechanics, the
states of a hydrogen atom that mimic classical elliptic orbits are the coherent
states of the SO(4) rotation group.It is known how to produce these states
experimentally. They have minimal dispersions of the two conserved vectors and
can be used as direction indicators. We compare the fidelity of this
transmission method with that of the idealized optimal method.
