The nitrogen-vacancy (NV) center in diamond is an attractive platform for quantum information and sensing applications because of its room temperature operation and optical addressability. A major research effort focuses on improving the quantum coherence of this defect in engineered micro- and nanoscale diamond particles (DPs), which could prove useful for high-resolution sensing in fluidic environments. In this work we fabricate cylindrical diamonds particles with finely tuned and highly reproducible sizes (diameter and height ranging from 100 to 700 and 500 nm to 2 μm, respectively) using high-purity, single-crystal diamond membranes with shallow-doped NV centers. We show that the spin coherence time of the NV centers in these particles exceeds 700 μs, opening the possibility for the creation of ultrahigh sensitivity micro- and nanoscale sensors. Moreover, these particles can be efficiently transferred into a water suspension and delivered to the region to probe. In particular, we introduce a DP suspension inside a microfluidic circuit and control position and orientation of the particles using an optical trapping apparatus. We demonstrate a DC magnetic sensitivity of 9 μT/√Hz in fluid as well as long-term trapping stability (>30 h), which paves the way toward the use of high-sensitivity pulse techniques on contactless probes manipulated within biological settings.
The nitrogen-vacancy (NV) center in diamond is an attractive platform for quantum information and sensing applications because of its room temperature operation and optical addressability. A major research effort focuses on improving the quantum coherence of this defect in engineered micro- and nanoscale diamond particles (DPs), which could prove useful for high-resolution sensing in fluidic environments. In this work we fabricate cylindrical diamonds particles with finely tuned and highly reproducible sizes (diameter and height ranging from 100 to 700 and 500 nm to 2 μm, respectively) using high-purity, single-crystal diamond membranes with shallow-doped NV centers. We show that the spin coherence time of the NV centers in these particles exceeds 700 μs, opening the possibility for the creation of ultrahigh sensitivity micro- and nanoscale sensors. Moreover, these particles can be efficiently transferred into a water suspension and delivered to the region to probe. In particular, we introduce a DP suspension inside a microfluidic circuit and control position and orientation of the particles using an optical trapping apparatus. We demonstrate a DC magnetic sensitivity of 9 μT/√Hz in fluid as well as long-term trapping stability (>30 h), which paves the way toward the use of high-sensitivity pulse techniques on contactless probes manipulated within biological settings.
High spatial resolution quantum sensing of near-surface nitrogen vacancy (NV) centers in diamond has enabled detection of magnetic, electrical, and thermal signals at the nanoscale. At depths of just a few nanometers, NV centers serve as localized quantum probes for external spins or low-dimensional materials, but their proximity to the surface also enhances decoherence caused by fluctuating nuclear spins. While advances in surface engineering have stabilized the charge state of NV centers at depths of tens of nanometers, achieving both ultra-shallow implantation (0.5-2 nm) and long-term spin coherence remains a central challenge. In this work, we show using first-principles modeling that, by exploiting the interaction of surface-induced strain and weak dc magnetic fields, the spin coherence times of 1-nm-deep NV centers can be greatly improved near the spin-phonon-confined regime at room temperature in 12C-rich diamonds. We also demonstrate that this protocol benefits ~ 10-nm-deep NV centers in natural diamond, enabling vector magnetometry at the nanoscale. Shallow NV centers in diamond are advantageous for quantum sensing but suffer from surface magnetic noise. Using first-principles simulations supported by experiments, the authors show that a combination of small magnetic fields and surface strain can significantly enhance spin coherence of 1 nm-deep NV centers.
The combination of long spin coherence time and nanoscale size has made nitrogen vacancy (NV) centers in nanodiamonds the subject of much interest for quantum information and sensing applications. However, currently available high-pressure high-temperature (HPHT) nanodiamonds have a high concentration of paramagnetic impurities that limit their spin coherence time to the order of microseconds, less than 1% of that observed in bulk diamond. In this work, we use a porous metal mask and a reactive ion etching process to fabricate nanocrystals from high-purity chemical vapor deposition (CVD) diamond. We show that NV centers in these CVD nanodiamonds exhibit record-long spin coherence times in excess of 200 μs, enabling magnetic field sensitivities of 290 nT Hz(-1/2) with the spatial resolution characteristic of a 50 nm diameter probe.
Diamond’s nitrogen-vacancy (NV) center has been shown as a promising candidate for sensing applications and quantum computing because of its long electron spin coherence time and its ability to be found, manipulated and read out optically. An integrated photonics platform in diamond would be useful for NV-based magnetometry and quantum computing, in which NV centers are optically linked for long-range quantum entanglement due to the integration and stability provided by monolithic optical waveguides. Surface microchannels in diamond would be a great benefit for sensing applications, where NV centers could be used to probe biomolecules. In this work, we applied femtosecond laser writing to form buried 3D optical waveguides in diamond. By engineering the geometry of the type II waveguide, we obtained single mode guiding from visible to the infrared wavelengths. Further, we demonstrate the first Bragg waveguide in bulk diamond with narrowband reflection. We show the formation of single, high quality NV centers on demand in ultrapure diamond using a single pulse from a femtosecond laser. With these building blocks in place, we fabricated an integrated quantum photonic circuit containing optical waveguides coupled to NV centers deterministically placed within the waveguide. The single NVs were excited and their emission collected by the optical waveguides, allowing easy interfacing to standard optical fibers. We also report high aspect ratio surface microchannels, which we will integrate with laser-written NVs and waveguides, paving the way for ultrasensitive, nanoscale resolution biosensors.
Deploying nitrogen vacancy (NV) centers in diamond as nanoscale quantum sensors for condensed matter and materials physics requires placing the NV centers close to the sensing target. One solution is to fabricate diamond nanostructures and integrate them with materials and devices. However, diamond etching and ion milling can introduce subsurface damage and surface defects that degrade the charge stability and spin coherence of NV centers near the surface. Here we report a procedure for fabricating low-damage nanostructured diamond membranes, and we show that this fabrication scheme preserves the optical and spin properties of state-of-the-art shallow NV center quantum sensors, within nanometers of the diamond surface, while providing significant photonic enhancement. Furthermore, we demonstrate a pick-and-place transfer method, which enables integration with diverse sensing targets.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
Individual, luminescent point defects in solids, so-called color centers, are atomic-sized quantum systems enabling sensing and imaging with nanoscale spatial resolution. In this overview, we introduce nanoscale sensing based on individual nitrogen vacancy (NV) centers in diamond. We discuss two central challenges of the field: first, the creation of highly-coherent, shallow NV centers less than 10 nm below the surface of a single-crystal diamond; second, the fabrication of tip-like photonic nanostructures that enable efficient fluorescence collection and can be used for scanning probe imaging based on color centers with nanoscale resolution.