  We demonstrate preferential orientation of nitrogen-vacancy (NV) color
centers along two of four possible crystallographic axes in diamonds grown by
chemical vapor deposition on the {100} face. We identify the relevant growth
regime and present a possible explanation of this effect. We show that
preferential orientation provides increased optical read-out contrast for NV
multi-spin measurements, including enhanced AC magnetic field sensitivity, thus
providing an important step towards high fidelity multi-spin-qubit quantum
information processing, sensing and metrology.
