  We propose a scheme to generate double electromagnetically induced
transparency and optimal cross-phase modulation for two slow, copropagating
pulses with matched group velocities in a single species of atom, namely 87 Rb.
A single pump laser is employed and a homogeneous magnetic field is utilized to
avoid cancellation effects through the nonlinear Zeeman effect. We suggest a
feasible preparational procedure for the atomic initial state to achieve
matched group velocities for both signal fields.
