  A method to determine the state of a single quantized cavity mode is
proposed. By adiabatic passage, the quantum state of the field is transfered
completely onto an internal Zeeman sub-manifold of an atom. Utilizing a method
of Newton and Young, we can determine this angular momentum state uniquely, by
a finite number of magnetic dipole measurements with Stern-Gerlach analyzers.
An example illustrates the influence of dissipation.
