  We study the exact dynamics of optical qubits encoded via coherent states
with opposite phases which are interacting with an environment modeled as a
collection of simple harmonic oscillators. Making use of a coherent-state path
integral formulation, we are able to study memory effects on the dynamics of
the coherent-state qubits due to strong environment coupling. We apply this
formulation to examine the time evolution of a noisy quantum channel formed by
two coherent-state qubits that are subject to uncorrelated local environment
noises. In particular, we examine the time evolution of entanglement and
maximal teleportation fidelity of the noisy quantum channel and show that at
strong coupling, due to large feedback effects from the environment noise, it
is possible to maintain a robust quantum channel in the long-time limit if
appropriate error-correcting code is applied.
