Nitrogen-vacancy centers in diamond have gained widespread attention as quantum systems that can be applied in quantum information devices. The excellent properties of quantum devices can be enhanced using preferentially oriented nitrogen-vacancy (NV) centers. However, thus far, orientation control has been achieved only via chemical vapor deposition. In this study, we demonstrate the creation of preferentially oriented NV centers via laser writing. The alignment ratio of ensemble NV centers is biased along the direction parallel to [111], depending on the femtosecond laser polarization, causing an increase of 55% in contrast to the optically magnetic resonance signal at maximum compared with 25% in random orientation. Based on time-dependent density-functional theory (TDDFT) simulations and experimental observations, such complex polarization dependence can be attributed to the anisotropy of electron excitation. This technique provides a new optical fabrication method for engineered materials and devices used in quantum technology.
The negatively charged nitrogen-vacancy (${\mathrm{NV}}^{\ensuremath{-}}$) center in diamond is an attractive candidate for applications that range from magnetometry to quantum information processing. Here we show that only a fraction of the nitrogen (typically
<0.5%) incorporated during homoepitaxial diamond growth by chemical vapor deposition (CVD) is in the form of undecorated ${\mathrm{NV}}^{\ensuremath{-}}$ centers. Furthermore, studies on CVD diamond grown on
(110)-oriented substrates show a near 100% preferential orientation of NV centers along only the
[111] and
[111] directions, rather than the four possible orientations. The results indicate that NV centers grow in as units, as the diamond is deposited, rather than by migration and association of their components. The NV unit of the ${\mathrm{NVH}}^{\ensuremath{-}}$ is similarly preferentially oriented, but it is not possible to determine whether this defect was formed by H capture at a preferentially aligned NV center or as a complete unit. Reducing the number of NV orientations from four orientations to two orientations should lead to increased optically detected magnetic resonance contrast and thus improved magnetic sensitivity in ensemble-based magnetometry.