  We propose an oversimplified scheme to unambiguously discriminate
nonorthogonal quantum field states inside high-Q cavities. Our scheme, which is
based on positive operator-valued mea- sures (POVM) technique, uses a single
three-level atom interacting resonantly with a single mode of a cavity-field
and selective atomic state detectors. While the single three-level atom takes
the role of the ancilla, the single cavity mode field represents the system we
want to obtain information. The efficiency of our proposal is analyzed
considering the nowadays achievements in the context of cavity QED.
