On the Formation of Dense Arrays of Nitrogen–Vacancy Centers in Synthetic Single-Crystal Diamonds for Quantum Sensors
Сергей Александрович Тарелкин, Stepan V. Bolshedvorskii, С.Г. Буга, Т. Е. Дроздова, Artem S. Galkin, Victor G. Vins, S.A. Nosukhin, Mikhail S. Kuznetsov, Dmitrii D. Prikhodko, V. S. Shcherbakova, Z. Liu, H. Kuo, Mingguang Yao
The dynamics of the formation of ensembles of nitrogen–vacancy color centers (NV centers) in single-crystal diamond plates after irradiation by high-energy (2 MeV) electrons and subsequent annealing is investigated. The concentration of the nitrogen impurity is determined from the infrared (IR) absorption spectrum to be 90 and 4 ppm for the diamond growth sectors {111} and {001}, respectively. The transverse relaxation times $$T_{2}^{*}$$ for the electron spin of NV centers are studied; they are found to amount to 200 and 900 ns for the {111} and {001} sectors, respectively, and are limited by the concentration of paramagnetic impurity defects in diamond. The sensitivity of quantum sensors based on the obtained ensembles of NV centers is estimated; the estimation shows feasibility of using denser ensembles in low-field magnetometry.
The dynamics of the formation of ensembles of nitrogen–vacancy color centers (NV centers) in single-crystal diamond plates after irradiation by high-energy (2 MeV) electrons and subsequent annealing is investigated. The concentration of the nitrogen impurity is determined from the infrared (IR) absorption spectrum to be 90 and 4 ppm for the diamond growth sectors {111} and {001}, respectively. The transverse relaxation times T2∗ for the electron spin of NV centers are studied; they are found to amount to 200 and 900 ns for the {111} and {001} sectors, respectively, and are limited by the concentration of paramagnetic impurity defects in diamond. The sensitivity of quantum sensors based on the obtained ensembles of NV centers is estimated; the estimation shows feasibility of using denser ensembles in low-field magnetometry.
NV- center has been paid attention as a quantum sensor for highly sensitive detection of magnetic field, electric field, temperature and strain, etc.. Electron beam irradiation followed by subsequent thermal annealing is known as the effective procedures to create NV- center in diamond. The electron irradiation generates vacancies in diamond and the annealing enables vacancies to diffuse in the lattice. Then diffused vacancies are captured by nitrogen atoms, and as a result, NV centers are created. In addition, substitutional nitrogen atom at a lattice site (P1 center) also acts as a donor for NV center, the charge state of NV centers changes from neutral (NV0) to NV-. Creation high concentration of ensemble NV- centers is needed to achieve high sensitively sensing. The magnetic sensitivity is proportional to the reciprocal of the number of NV centers and T2 (spin coherence time), i.e., high concentration NV- centers with long T2 increase the sensitivity. P1 center has an important role for being a component of NV- centers and acting as donor to the NV center. But it also plays a role as decoherence source (decrease in magnetic field sensitivity). Therefore, it is important to create high concentration of NV- centers considering the amount of P1 centers. In current study, we investigate irradiation fluence dependence of the creation behavior of NV centers in type-Ib diamonds by using electron spin resonance (ESR) and photo-luminescence (PL) to understand the creation mechanism of NV- center. The values of T2 are also evaluated by Hahn-echo measurement, since it is one of the key parameters for highly sensitive magnetometry. Then, we discuss the creation mechanism of NV centers based on concentrations of defects.
Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.
Abstract Negatively charged nitrogen-vacancy (NV − ) center ensembles in diamond have proved to have great potential for use in highly sensitive, small-package solid-state quantum sensors. One way to improve sensitivity is to produce a high-density NV − center ensemble on a large scale with a long coherence lifetime. In this work, the NV − center ensemble is prepared in type-Ib diamond using high energy electron irradiation and annealing, and the transverse relaxation time of the ensemble— T 2 —was systematically investigated as a function of the irradiation electron dose and annealing time. Dynamical decoupling sequences were used to characterize T 2 . To overcome the problem of low signal-to-noise ratio in T 2 measurement, a coupled strip lines waveguide was used to synchronously manipulate NV − centers along three directions to improve fluorescence signal contrast. Finally, NV − center ensembles with a high concentration of roughly 10 15 mm −3 were manipulated within a ~10 µ s coherence time. By applying a multi-coupled strip-lines waveguide to improve the effective volume of the diamond, a sub-femtotesla sensitivity for AC field magnetometry can be achieved. The long-coherence high-density large-scale NV − center ensemble in diamond means that types of room-temperature micro-sized solid-state quantum sensors with ultra-high sensitivity can be further developed in the near future.
Abstract The nitrogen-vacancy (NV) center in diamond is a promising quantum system for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels. Key material requirements for NV ensembles are a high NV − concentration, a long spin coherence time and a stable charge state. However, these are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. In this work, we systematically investigate the NV center formation and properties in bulk chemical vapor deposition (CVD) diamond. The nitrogen flow during growth is varied by over four orders of magnitude, resulting in a broad range of single substitutional nitrogen concentrations of 0.2–20 parts per million. For a fixed nitrogen concentration, we optimize electron-irradiation fluences with two different accelerated electron energies, and we study defect formation via optical characterizations. We discuss a general approach to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. We achieve spin–spin coherence times T 2 ranging from 45.5 to 549 μ s for CVD diamonds containing 168 to 1 parts per billion NV − centers, respectively. This study shows a pathway to engineer properties of NV-doped CVD diamonds for improved sensitivity.
Currently, synthetic diamonds are finding new applications. Quantum devices can be created based on diamond plates with the desired concentration of defects in the structure of the crystal lattice. NV color centers can be used in quantum applications by irradiating plates with high-energy particles, followed by annealing at temperatures above 800°C to develop the spin-optical properties of the centers Diamond plates are subjected to electron irradiation and much less often to proton irradiation. As a result, synthetic diamond plates with NV centers ob-tained by proton irradiation are less studied, although proton irradiation makes it possible to obtain a layered structure of NV centers. In this work, single crystal diamond plates irradiated with protons were studied using polarization microscopy, IR spectroscopy and ODMR spectros-copy. It is shown that when creating NV centers, the distribution and concentration of C – defects in the sample, as well as mechanical stresses before and after irradiation (with subsequent an-nealing), can differ significantly from each other.
Among quantum sensors, the single nitrogen-vacancy (NV) defect in diamond has the highest sensitivity-to-size factor. For instance, a single-NV spin when used as a magnetometer could achieve sensitivities of the order of nT/Hz, while the dimensions of the sensor are merely atomic in size. The sensitivity is limited only by the photon shot noise. One method to boost the magnetometer sensitivity to pico-tesla scales is to use many NV defect centers as an ensemble sensor [Phys. Rev. X5, 041001 (2015)PRXHAE2160-330810.1103/PhysRevX.5.041001]. However, during the absorption-emission (fluorescence) optical cycles, the NV centers transfer a portion of the irradiation laser energy into phonons and heat the diamond matrix. This results in unintended fluorescence decrease, spin resonance lines shifts, and fluctuations. Hence, the advantages gained by packing a high density of NV centers are significantly reduced. Here we investigate the heat generation of ensemble NV centers in micrometer-sized diamond under 532 nm laser irradiation and its effects pertaining to sensing applications. These investigations help us to find strategies that mitigate the detrimental effects of heating and yet permits the use of ensemble NV defects for improved metrology applications.