  In this paper we investigate the generation of entanglement between two
persistent current qubits. The qubits are coupled inductively to each other and
to a common bias field, which is used to control the qubit behaviour and is
represented schematically by a linear oscillator mode. We consider the use of
classical and quantum representations for the qubit control fields and how
fluctuations in the control fields tend to suppress entanglement. In
particular, we demonstrate how fluctuations in the bias fields affect the
entanglement generated between persistent current qubits and may limit the
ability to design practical systems.
