Seeing the forbidden: overcoming optical selection rules through nanophotonic integration

TL;DR

This paper demonstrates that nanophotonic structures like nanopillars can modify local electromagnetic environments, enabling optical access to defect transitions suppressed in bulk silicon carbide, thus advancing quantum defect spectroscopy.

Contribution

It reveals how nanopillars alter electromagnetic fields to activate dark defect transitions and resolve spectral ambiguities in silicon carbide quantum defects.

Findings

Enhanced emission from PL3 divacancy in nanopillars due to polarization transformation.

Resolved the origin of spectral lines, confirming NV4' as a higher excited state of the kh defect.

Nanophotonic integration acts as a symmetry-sensitive probe for defect states.

Abstract

Optically addressable spin defects in silicon carbide, including the neutral divacancy (VV$^0$) and the negative nitrogen-vacancy (NV$^-$), are among leading building blocks of solid-state quantum technologies. Integrating these defects into photonic structures such as nanopillars improves photon collection efficiency, but the consequences extend further. We show that the sub-wavelength geometry of nanopillars drastically modifies the local electromagnetic environment, providing optical access to defect transitions that are otherwise suppressed by selection rules in bulk material. Using low-temperature photoluminescence spectroscopy, we observe that emission from the PL3 divacancy, which is nearly absent in planar devices, becomes pronounced in nanopillars owing to a polarization transformation of the excitation field within the pillar. We further leverage the orientation-dependent collection of nanopillars to resolve the origin of previously ambiguous spectral lines. In particular, the NV4$'$ feature displays the signal enhancement expected for axially oriented NV$^-$ centres, consistent with assignment to a higher excited state of the $kh$ defect configuration. Our results establish nanophotonic integration as a symmetry-sensitive probe that can both activate nominally dark transitions and identify the dipole character of poorly understood defect states.