  We analyze the entanglement evolution of two cavity photons being affected by
the dissipation of two individual reservoirs. Under an arbitrary local unitary
operation on the initial state, it is shown that there is only one parameter
which changes the entanglement dynamics. For the bipartite subsystems, we show
that the entanglement of the cavity photons is correlated with that of the
reservoirs, although the local operation can delay the time at which the photon
entanglement disappears and advance the time at which the reservoir
entanglement appears. Furthermore, via a new defined four-qubit entanglement
measure and two three-qubit entanglement measures, we study the multipartite
entanglement evolution in the composite system, which allows us to analyze
quantitatively both bipartite and multipartite entanglement within a unified
framework. In addition, we also discuss the entanglement evolution with an
arbitrary initial state.
