  We discuss a practical design for tunably coupling a pair of flux qubits via
the quantum inductance of a third high-frequency qubit. The design is
particularly well suited for realizing a recently proposed microwave-induced
parametric coupling scheme. This is attractive because the qubits can always
remain at their optimal points. Furthermore, we will show that the resulting
coupling also has an optimal point where it is insensitive to low-frequency
flux noise. This is an important feature for the coherence of coupled qubits.
The presented scheme is an experimentally realistic way of carrying out
two-qubit gates and should be easily extended to multiqubit systems.
