  We show that two capacitively-coupled Josephson junctions, in the quantum
limit, form a simple coupled qubit system with effective coupling controlled by
the junction bias currents. We compute numerically the energy levels and wave
functions for the system, and show how these may be tuned to make optimal
qubits. The dependence of the energy levels on the parameters can be measured
spectroscopically, providing an important experimental test for the presence of
entangled multiqubit states in Josephson-junction based circuits.
