  Stationary photon-atom entanglement is discussed by applying the method of
flow equation to the Jaynes-Cummings model. A nonlocal continuous unitary
transformation is explicitly constructed and the associated positive
operator-valued measures for the photons and atom are obtained. Then, flow of
the entanglement entropy is analyzed. A comment is also made on implementing
the unitary operation in the method of flow equation. This method may offer a
new strategy for quantum-state engineering.
