  An entangled two-mode coherent state is studied within the framework of
$2\times 2$ dimensional Hilbert space. An entanglement concentration scheme
based on joint Bell-state measurements is worked out. When the entangled
coherent state is embedded in vacuum environment, its entanglement is degraded
but not totally lost. It is found that the larger the initial coherent
amplitude, the faster entanglement decreases. We investigate a scheme to
teleport a coherent superposition state while considering a mixed quantum
channel. We find that the decohered entangled coherent state may be useless for
quantum teleportation as it gives the optimal fidelity of teleportation less
than the classical limit 2/3.
