  We demonstrate that Zeeman ground-state spin levels in Nd3+:YVO4 provides the
possibility to create an efficient lambda-system for optical pumping
experiments. The branching ratio R in the lambda-system is measured
experimentally via absorption spectroscopy and is compared to a theoretical
model. We show that R can be tuned by changing the orientation of the magnetic
field. These results are applied to optical pumping experiments, where
significant improvement is obtained compared to previous experiments in this
system. The tunability of the branching ratio in combination with its good
coherence properties and the high oscillator strength makes Nd3+:YVO4 an
interesting candidate for various quantum information protocols.
