Nitrogen-vacancy (NV) centers in diamond photonic nanostructures have attracted much attention as efficient single photon emitters and quantum bits. These quantum optical devices mostly require single or low-density NV centers doped in thin diamond membranes. In contrast, this study focuses on diamond photonic nanostructures with a high concentration of NV centers to achieve a diamond color center laser with a sufficient gain available as a visible light source and a sensitive magnetic-field sensor. We employ high-dose helium ion implantation to type-Ib diamond substrates and thermal annealing, which enables us to obtain uniform thin diamond membranes containing a dense ensemble of NV centers. Luminescence spectroscopy reveals the kinetics of NV centers at high temperature from which we find an optimum annealing temperature maximizing the NV center emission while suppressing the transformation from NV to H3 centers. Furthermore, fine photonic nanowires are also successfully fabricated in the air-suspended diamond membrane, and they exhibit intense photoluminescence from the NV centers with a concentration as high as 7 × 1016 cm−3 (0.4 ppm). These results suggest a route to the fabrication of diamond photonic nanostructures containing a dense ensemble of NV centers, which can be a key material for developing diamond-based light emitting and magnetic-field sensing devices.
Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon-vacancy centers have been shown to operate at temperatures beyond 1 K without phonon-mediated decoherence. In this work, we combine high-stress silicon-nitride thin films with diamond nanostructures to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of ∼4×10−4. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5 K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well.
Silicon-vacancy (SiV) color centers in diamond offer novel possibilities to probe light-matter interaction in nano-quantum optics and provide a scalable quantum system suitable for single-photon emission. However, their effective count-rate is still limited by non-radiative decay channels, radiation at wide angles and total internal reflection at the diamond interface. Recently optical antennas have been utilized in order to modify light-matter interaction at the nanoscale. Acting as resonators, they are able to increase the spontaneous emission rate of quantum emitters by several orders of magnitude in a broad spectral range. Because coupling a quantum emitter to a nano-antenna requires close proximity between the two systems, we implant Si ions on very thin diamond membranes that provide the required dimension for near-field interaction in a controlled manner and investigate the optical properties of SiV color centers in such diamond membranes. We consider gold nano-cones as nano-antennas, fabricated by focused electron beam induced deposition (EBID), followed by sputtering and focused ion beam (FIB) milling. The finite-difference time-domain (FDTD) calculations show that gold nano-cones can provide more than four orders of magnitude enhancement in the Purcell factor with an antenna efficiency (AE) of 80%.