Deterministic enhancement of coherent photon generation from a nitrogen-vacancy center in ultrapure diamond (1703.00815v1)

Abstract: The nitrogen-vacancy (NV) center in diamond has an optically addressable, highly coherent spin. However, an NV center even in high quality single-crystalline material is a very poor source of single photons: extraction out of the high-index diamond is inefficient, the emission of coherent photons represents just a few per cent of the total emission, and the decay time is large. In principle, all three problems can be addressed with a resonant microcavity. In practice, it has proved difficult to implement this concept: photonic engineering hinges on nano-fabrication yet it is notoriously difficult to process diamond without degrading the NV centers. We present here a microcavity scheme which uses minimally processed diamond, thereby preserving the high quality of the starting material, and a tunable microcavity platform. We demonstrate a clear change in the lifetime for multiple individual NV centers on tuning both the cavity frequency and anti-node position, a Purcell effect. The overall Purcell factor $F_{\rm P}=2.0$ translates to a Purcell factor for the zero phonon line (ZPL) of $F_{\rm P}^{\rm ZPL}\sim30$ and an increase in the ZPL emission probability from $\sim 3 \%$ to $\sim 46 \%$. By making a step-change in the NV's optical properties in a deterministic way, these results pave the way for much enhanced spin-photon and spin-spin entanglement rates.

Deterministic Enhancement of Coherent Photon Generation from NV Centers in Diamond

This paper investigates the deterministic enhancement of coherent photon generation from nitrogen-vacancy (NV) centers in ultrapure diamond using resonant microcavity technology. NV centers are pivotal in quantum technology due to their optically addressable, coherent electron spin characteristics. Despite these advantages, NV centers traditionally exhibit low photon extraction efficiency from the high-index diamond, minimal coherent photon emission, and substantial decay times.

The researchers address these limitations through a microcavity scheme employing minimally processed diamond and a tunable microcavity platform. The experiments demonstrate a significant change in NV center lifetimes upon tuning both the cavity frequency and anti-node position, indicative of the Purcell effect. Specifically, the overall Purcell factor $F_{\rm P} = 2.0$ correlates to a Purcell factor for the zero phonon line (ZPL), $F_{\rm P}^{\rm ZPL} \approx 30$, with ZPL emission probability increasing from approximately 3% to roughly 46%.

The findings suggest a deterministic step-change enhancement in NV's optical properties, demonstrating considerable potential for improved spin-photon and spin-spin entanglement rates. This is particularly relevant for quantum teleportation and long-distance spin-spin entanglement protocols, offering a solution to the low generation rate of indistinguishable photons from NV centers.

Theoretical calculations align closely with experimental results, showing that the enhanced emission rates correlate with the microcavity design, particularly the vacuum electric field at the anti-node. The scalability and design flexibility of the miniaturized Fabry-Pérot microcavity make it an attractive platform for advancing quantum technology applications, extending to other color centers and materials like SiC.

Speculative implications suggest that with technical improvements in the cavity design and optimal NV placement, it may be possible to achieve near-perfect ZPL photonic emission efficiencies. Such advances could drastically increase photon indistinguishability and, consequently, the rates of entanglement in quantum networks.

By leveraging advancements in microfabrication and the inherent properties of high-quality diamond, this work offers promising pathways for efficient quantum information processing and communication, thus paving the way for robust quantum networks.