  In superconducting circuits with interbit untunable (e.g., capacitive)
couplings, ideal local quantum operations cannot be exactly performed on
individual Josephson qubits. Here we propose an effective dynamical decoupling
approach to overcome the "fixed-interaction" difficulty for effectively
implementing elemental logical gates for quantum computation. The proposed
single-qubit operations and local measurements should allow testing Bell's
inequality with a pair of capacitively-coupled Josephson qubits. This provides
a powerful approach, besides spectral-analysis [Nature \textbf{421}, 823
(2003); Science \textbf{300}, 1548 (2003)], to verify the existence of
macroscopic quantum entanglement between two fixed-coupling Josephson qubits.
