  We study the entanglement of a pair of qubits resulting from their
interaction with a bosonic system. Here we restrict our discussion to the case
where the set of operators acting on different qubits commute. A special class
of interactions inducing entanglement in an initially separable two qubit
system is discussed. Our results apply to the case where the initial state of
the bosonic system is represented by a statistical mixture of states with fixed
particle number.
