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AVS Quantum Science

Unveiling the high quantum efficiency of single silicon-vacancy centers through dielectric tuning of their local environment

M. Bézard, Yuliya Mindarava, Rémi Blinder, Jean-Baptiste Trebbia, Philippe Tamarat, Fedor Jelezko, Brahim Lounis

Published Sep 1, 2024• 4 citations
Publisher

Abstract

We use a simple and effective experimental method for determining the radiative quantum yield of single silicon-vacancy centers (SiV) in nanometric-sized diamonds (NDs). It is based on variations in the luminescence lifetimes of SiVs induced by a controlled change in the NDs' dielectric environment. The deposition of a high refractive index immersion oil on a thin polymer sample containing NDs with an average size of 20 nm induces a noticeable shortening of SiV lifetimes, a clear signature of a strong radiative contribution to the decays. While SiV centers were generally considered to be weak quantum emitters, we demonstrate that single SiV centers in nanodiamonds have a quantum efficiency up to 60%, under ambient conditions. This quantum efficiency is very similar to that of the negatively charged nitrogen-vacancy centers, which we measured using the same approach. This feature makes single SiV attractive as bright, high-purity single-photon sources for quantum technologies.

DOI
10.1116/5.0216709

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Journal of Physics Conference Series•Jul 1, 2026•0 citations
We use a simple and effective experimental method for determining the radiative quantum yield of single silicon-vacancy centers (SiV) in nanometric-sized diamonds (NDs). It is based on variations in the luminescence lifetimes of SiVs induced by a controlled change in the NDs' dielectric environment. The deposition of a high refractive index immersion oil on a thin polymer sample containing NDs with an average size of 20 nm induces a noticeable shortening of SiV lifetimes, a clear signature of a strong radiative contribution to the decays. While SiV centers were generally considered to be weak quantum emitters, we demonstrate that single SiV centers in nanodiamonds have a quantum efficiency up to 60%, under ambient conditions. This quantum efficiency is very similar to that of the negatively charged nitrogen-vacancy centers, which we measured using the same approach. This feature makes single SiV attractive as bright, high-purity single-photon sources for quantum technologies.
Nitrogen–vacancy (NV) centers in diamond are generally recognized as highly promising as indefinitely stable highly efficient single-photon sources. We report an experimental quantification of the brightness, radiative decay rate, nonradiative decay rate and quantum efficiency of single NV centers in diamond nanocrystals. Our experiments show that the commonly observed large spread in fluorescence decay rates of NV centers in nanodiamond is inconsistent with the common explanation of large nanophotonic mode-density variations in the ultra-small high-index crystals at near-unity quantum efficiency. We report that NV centers in 25 nm nanocrystals are essentially insensitive to local density of optical states (LDOS) variations that we induce at a dielectric interface by using liquids to vary the refractive index, and propose that quantum efficiencies in such nanocrystals are widely distributed between 0 and 20%. For single NV centers in larger 100 nm nanocrystals, we show that decay rate changes can be reversibly induced by nanomechanically approaching a mirror to change the LDOS. Using this scanning mirror method, for the first time we report calibrated quantum efficiencies of NV centers, and show that different but nominally identical nanocrystals have widely distributed quantum efficiencies between 10 and 90%. Our measurements imply that nanocrystals that are to be assembled into hybrid photonic structures for cavity QED should first be individually screened to assess fluorescence properties in detail.
The negatively-charged nitrogen vacancy (NV(-)) center in diamond is of great interest for quantum information processing and quantum key distribution applications due to its highly desirable long coherence times at room temperature. One of the challenges for their use in these applications involves the requirement to further optimize the lifetime and emission properties of the centers. Our results demonstrate the reduction of the lifetime of NV(-) centers, and hence an increase in the emission rate, achieved by modifying the refractive index of the environment surrounding the nanodiamond (ND). By coating the NDs in a polymer film, experimental results and numerical calculations show an average of 63% reduction in the lifetime and an average enhancement in the emission rate by a factor of 1.6. This strategy is also applicable for emitters other than diamond color centers where the particle refractive index is greater than the refractive index of the surrounding media.
Understanding and mastering quantum electrodynamics phenomena is essential to the development of quantum nanophotonics applications. While tailoring of the local vacuum field has been widely used to tune the luminescence rate and directionality of a quantum emitter, its impact on their transition energies is barely investigated and exploited. Fluorescent defects in nanosized diamonds constitute an attractive nanophotonic platform to investigate the Lamb shift of an emitter embedded in a dielectric nanostructure with high refractive index. Using spectral and time-resolved optical spectroscopy of single SiV defects, we unveil blue shifts (up to 80 meV) of their emission lines, which are interpreted from model calculations as giant Lamb shifts. Moreover, evidence for a positive correlation between their fluorescence decay rates and emission line widths is observed, as a signature of modifications not only of the photonic local density of states but also of the phononic one, as the nanodiamond size is decreased. Correlative light-electron microscopy of single SiVs and their host nanodiamonds further supports these findings. These results make nanodiamond-SiVs promising as optically driven spin qubits and quantum light sources tunable through nanoscale tailoring of vacuum-field fluctuations.
The charge dynamics of silicon-vacancy (SiV) centers have been investigated for the first time in high-pressure high-temperature nanodiamonds (NDs) with varying concentrations of substitutional nitrogen (Ns). We demonstrate a controlled sixfold enhancement of SiV- photoluminescence (PL) under dual-color excitation, consisting of strong red (~660 nm) illumination combined with weak green (~530 nm) excitation. The measured dependencies of SiV- PL lifetime and intensity on excitation wavelength, together with the enhancement dependence on Ns concentration in the studied nanodiamonds, provide unambiguous evidence of the involvement of donor nitrogen in SiV-emission dynamics. Saturation curves and second-order PL intensity correlation measurements further indicate suppression of the population of the optically inactive SiV2- state upon the addition of green excitation. These results unlock a practical pathway toward engineering optically-controlled and scalable quantum emitters based on SiV-luminescent diamond nanoparticles.
The nitrogen vacancy (NV) center is the most widely studied single optical defect in diamond with great potential for applications in quantum technologies. Development of practical single-photon devices requires an understanding of the emission under a range of conditions and environments. In this work, we study the properties of a single NV center in nanodiamonds embedded in an air-like silica aerogel environment which provides a new domain for probing the emission behavior of NV centers in nanoscale environments. In this arrangement, the emission rate is governed primarily by the diamond crystal lattice with negligible contribution from the surrounding environment. This is in contrast to the conventional approach of studying nanodiamonds on a glass coverslip. We observe an increase in the mean lifetime due to the absence of a dielectric interface near the emitting dipoles and a distribution arising from the irregularities in the nanodiamond geometry. Our approach results in the estimation of the mean quantum efficiency (~0.7) of the nanodiamond NV emitters.
Abstract Single photon sources (SPSs) are one of the key components in quantum communication technology. Here we report on the development of a new approach to the controlled formation of SPSs in nanodiamonds synthesized from hydrocarbons at high pressure and high temperature (HPHT). The conditions of HPHT synthesis were determined, allowing for the highly efficient production of scalable single-photon emitters based on single silicon-vacancy (SiV) centers in individual diamond particles of 250-300 nm in size. A new type of SPSs, emitting in a wide spectral range (500-800 nm) at room temperature, was found in hydrogen-terminated nanodiamonds. The recorded rate of the SPS emission exceeds 1 million photons per second. The HPHT nanodiamonds containing both SiV and the new emitters are a promising material for quantum photonics applications.