Ensembles of nitrogen-vacancy (NV) centers in diamond are a leading platform for sensing and imaging magnetic fields at room temperature, in part due to advances in diamond growth. An essential step to improving diamond material involves the characterization of crystal and NV-related properties, such as strain and paramagnetic impurities, which can shift and broaden the NV resonances used for sensing. Full sample characterization through wide-field imaging enables both fast and detailed feedback for growers, along with the estimation of sensing performance before use. We present a quantum diamond microscope tailored for millimeter-scale wide-field mapping of key quantum properties of NV-diamond chips, including NV ensemble photoluminescence intensity, spin-lattice relaxation time (T1), and spin-coherence lifetimes (T2 and T2*). Our design also allows for lattice stress/strain and birefringence magnitude/angle mapping, and their in situ correlation with NV properties.
Ensembles of nitrogen-vacancy (NV) centers in diamond are a leading platform for sensing and imaging magnetic fields at room temperature, in part due to advances in diamond growth. An essential step to improving diamond material involves the characterization of crystal and NV-related properties, such as strain and paramagnetic impurities, which can shift and broaden the NV resonances used for sensing. Full sample characterization through wide-field imaging enables both fast and detailed feedback for growers, along with the estimation of sensing performance before use. We present a quantum diamond microscope tailored for millimeter-scale wide-field mapping of key quantum properties of NV-diamond chips, including NV ensemble photoluminescence intensity, spin-lattice relaxation time (T1), and spin-coherence lifetimes (T2 and T2*). Our design also allows for lattice stress/strain and birefringence magnitude/angle mapping, and their in situ correlation with NV properties.
Nitrogen-vacancy (NV) centers in diamond are a leading modality for magnetic sensing and imaging under ambient conditions. However, these sensors suffer from degraded performance due to paramagnetic impurities and regions of stress in the diamond crystal lattice. This work demonstrates a quantum diamond microscope (QDM) for simultaneous mapping and spatial correlation of key properties of a millimeter-scale NV-diamond sensor chip, including: NV ensemble photoluminescence (PL) amplitude, spin-lattice relaxation time (T1), and homogeneous and inhomogeneous spin coherence lifetimes (T2 and T2∗), as well as lattice stress/strain, birefringence magnitude, and birefringence angle of the diamond crystal.
Crystal-strain variation imposes significant limitations on many quantum sensing and information applications for solid-state defect qubits in diamond. Thus, the precision measurement and control of diamond crystal strain is a key challenge. Here, we report diamond strain measurements with a unique set of capabilities, including micron-scale spatial resolution, a millimeter-scale field of view, and a 2-order-of-magnitude improvement in volume-normalized sensitivity over previous work, reaching $5(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}/\sqrt{\mathrm{Hz}\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}3}}$ (with spin-strain coupling coefficients representing the dominant systematic uncertainty). We use strain-sensitive spin-state interferometry on ensembles of nitrogen-vacancy (N-V) color centers in single-crystal bulk diamond with low strain gradients. This quantum interferometry technique provides insensitivity to magnetic-field inhomogeneity from the electronic and nuclear spin bath, thereby enabling long N-V--ensemble electronic spin dephasing times and enhanced strain sensitivity, as well as broadening the potential applications of the technique beyond isotopically enriched or high-purity diamond. We demonstrate the strain-sensitive measurement protocol first on a confocal scanning laser microscope, providing quantitative measurement of sensitivity as well as three-dimensional strain mapping; and second on a wide-field-imaging quantum diamond microscope. Our strain-microscopy technique enables fast, sensitive characterization for diamond material engineering and nanofabrication; as well as diamond-based sensing of strains applied externally, as in diamond anvil cells or embedded diamond stress sensors, or internally, as by crystal damage due to particle-induced nuclear recoils.
Ensembles of nitrogen-vacancy (NV) centers in diamond are versatile quantum sensors with broad applications in the physical and life sciences. The concentration of neutral substitutional nitrogen ( [ N s 0 ]) strongly influences NV electronic spin coherence times, sensitivity, and optimal sensing strategies. Diamonds with [ N s 0 ] ∼ 1–10 ppm are a focus of recent material engineering efforts, with higher concentrations being favorable for continuous-wave optically detected magnetic resonance (CW-ODMR) and lower concentrations expected to benefit pulsed magnetometry techniques through extended NV spin coherence times and improved sensing duty cycles. In this work, we synthesize and characterize low- [ N s 0 ] ( ∼ 0.8 ppm), NV-enriched diamond material, engineered through low-strain chemical vapor deposition (CVD) growth on high-quality substrates, 12 C isotopic purification, and controlled electron irradiation and annealing. Our results demonstrate good strain homogeneity in diamonds grown on CVD substrates and spin-bath-limited NV dephasing times. By measuring NV spin and charge properties across a wide range of optical NV excitation intensity, we provide direct comparisons of photon-shot-noise-limited magnetic field sensitivity between the current low- [ N s 0 ] and previously studied higher- [ N s 0 ] ( ∼ 14 ppm) NV-diamond sensors. We show that low- [ N s 0 ] diamond can outperform higher- [ N s 0 ] diamond at moderate and low optical NV excitation intensity. Our results provide practical benchmarks and guidance for selecting NV-diamond sensors tailored to specific experimental constraints and sensing requirements.
In recent years, nitrogen-vacancy (NV) color centers in diamond have become excellent solid-state quantum sensors due to their electronic spin properties. Especially for their easy optical initialization and detection, together with their very large spin coherence at room temperature. Many studies have reported their use for sensing temperature, strain, electric fields, and mainly magnetic fields. Here, we show how to build a two-dimensional map of the electronic spin coherence of an ensemble of NV centers in ultra-pure diamond, using an optical imaging protocol combined with microwave pulses relying simply on a regular CCD camera.
Quantum sensors utilize quantized energy levels, quan- tum superposition states, and eventually quantum entan- glement, which are also key elements in quantum comput- ing. Electronic and nuclear spins in semiconductors may serve as quantum sensing elements or qubits. The phos- phorus donor in silicon is an ideal qubit in terms of coherence time because of highest chemical purity of host material with isotopic 28Si enrichment and a very low den- sity of structural defects. However, it requires a cryogenic temperature to avoid ionization of the donor. In contrast in diamond, due to the wide band gap, the nitrogen-vacancy (NV) center exhibits optical initialization and readout of its spin state and a long coherence time even above room temperature, promoting its research and development as quantum sensors or qubits. Nevertheless, the syn- thesized diamond crystals with NV centers are not so per- fect as silicon. Therefore, the host material characteriza- tion is essential to improve the bulk-ensemble sensi- tivity to the magnetic field. The present study shows how to measure the spin properties of the diamond as a sens- ing host via the NV centers themselves and how to utilize such information to improve the sensor performance.
Among the possible defects that can occur in diamonds, one that draws attention is the nitrogen-vacancy (NV) center.Studied since the early 90s, in recent years, they became one of the most promising platforms for field applications of quantum technology at room temperature, especially for quantum sensing.They are sensitive to electric and magnetic fields, temperature, and strain, making these nanosensors a versatile platform for many applications.The NV center's spin state is easy to read and manipulate by optical means, and, most interestingly, it works well at room temperature, which facilitates its use.The great challenge to implement quantum protocols and quantum algorithms is the coherence time of the quantum states.The NV center stands out for having relatively high coherence times at room temperature.This dissertation presents measurements to characterize the electron spin coherence of NV centers in an ultrapure sample of diamond designed for quantum sensing applications.These measurements combine optical e magnetic resonance techniques.For that, a method was implemented using a conventional CCD camera and a clever imaging protocol, making it possible to perform various pulsed microwave experiments on the electron spin, such as Rabi oscillations and Hahn spin-echo, which were used for determining the characteristic relaxation times (T 1 and T 2 ).Results show that this system provides at least two readily accessible qubits that can be used in quantum protocols even at room temperature.