Efficient optical pumping of Zeeman spin levels in

We demonstrate that Zeeman ground-state spin levels in Nd 3 + : YVO 4 provides the possibility to create an efficient Λ - system for optical pumping experiments. The branching ratio R in the Λ -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 Nd 3 + : YVO 4 an interesting candidate for various quantum information protocols.