  We develop a geometric approach to quantify the capability of creating
entanglement for a general physical interaction acting on two qubits. We use
the entanglement measure proposed by us for $N$-qubit pure states (PRA
\textbf{77}, 062334 (2008)). Our procedure reproduces the earlier results (PRL
\textbf{87}, 137901 (2001)). The geometric method has the distinct advantage
that it gives an experimental way to monitor the process of optimizing
entanglement production.
