Single nitrogen vacancy centers in chemical vapor deposited diamond nanocrystals (0706.2518v2)

Abstract: Nanodiamond crystals containing single color centers have been grown by chemical vapor deposition (CVD). The fluorescence from individual crystallites was directly correlated with crystallite size using a combined atomic force and scanning confocal fluorescence microscope. Under the conditions employed, the optimal size for single optically active nitrogen-vacancy (NV) center incorporation was measured to be 60 to 70 nm. The findings highlight a strong dependence of NV incorporation on crystal size, particularly with crystals less than 50 nm in size.

Overview of "Single Nitrogen Vacancy Centers in Chemical Vapor Deposited Diamond Nanocrystals"

This paper elucidates a systematic paper of the incorporation of single nitrogen-vacancy (NV) centers in diamond nanocrystals synthesized via the chemical vapor deposition (CVD) technique. The significance of this research lies in the role NV centers in diamond play, particularly in quantum information processing as reliable single-photon sources and potential qubits, making this paper pertinent for advancements in quantum computing and bio-labeling applications.

Methodology

The research utilizes a combined atomic force microscopy (AFM) and confocal fluorescence microscopy approach to directly correlate the fluorescence properties of individual nanocrystals with their sizes. CVD technique was employed for the synthesis, with particular attention given to nitrogen incorporation, which is customary in diamond lattice due to its natural abundance. An ASTeX microwave plasma chemical vapor deposition reactor was used under controlled conditions to grow diamond nanocrystals on quartz substrates, optimizing parameters to induce the formation of NV centers.

Key Findings

• Optimal Crystal Size: It was determined that single NV centers are preferentially incorporated in diamond crystals with diameters ranging from 60 to 70 nanometers. The paper reveals that the probability of observing NV centers diminishes significantly for crystals smaller than 40 nm.
• Incorporation Efficiency: The research highlights a critical efficiency metric where the conversion of nitrogen atoms from the gas phase into NV centers is notably low, of the order of $5 \times 10^{-8}$. Notably, raising the nitrogen-to-carbon (N/C) ratio beyond 0.2 degrades the CVD diamond quality without significantly enhancing NV incorporation.
• Fluorescence and Coherence Properties: At cryogenic temperatures, the NV centers demonstrated broadened spectral lines due to ionization-induced spectral diffusion. The spin coherence lifetime $T_2$ was observed to be substantially lower compared to that in ultrapure single-crystal diamonds, signaling potential decoherence mechanisms operative at high nitrogen concentrations.

Implications and Speculations

The findings of this paper offer valuable insights into the material grow tactics required for the effective realization of single NV centers in nanodiamonds. This has significant implications for the scalability of quantum information systems. The ability to synthesize isolated, single-NV nanocrystals on diverse substrates extends potential applications in quantum computing for spin-based entanglement and communications.

From a materials science perspective, this paper underscores critical areas requiring further inquiry, such as the influence of surface defects on NV emission quenching and the interaction of NV centers with proximate impurities. The constraints posed by decoherence in NV spin states invite future explorations into reducing impurity concentrations during the synthesis phase, potentially augmenting coherence times.

This paper signifies an advancement both in the understanding and in practical methodologies for manipulating sub-micron diamond materials. Researchers are encouraged to pursue further refinements in nitrogen and $^{13}$C isotope control during CVD, aiming to optimize quantum coherence dynamics and encompass broader applications in biological fluorescence labeling.

Conclusion

This paper marks a substantive contribution to the field of quantum materials science, enabling deeper engagement with the quantum information applications of diamond NV centers. Exploring the intricate dependencies of NV center incorporation on nanocrystal size lays a foundation for future research aimed at enhancing the utility of these quantum systems in both computational and biophysical contexts.