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Register a new userEnhanced widefield quantum sensing with nitrogen-vacancy ensembles using diamond nanopillar arrays
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Quantum sensors based on optically active defects in diamond such as the nitrogen vacancy (NV) centre represent a promising platform for nanoscale sensing and imaging of magnetic, electric, temperature and strain fields. Enhancing the optical interface to such defects is key to improving the measurement sensitivity of these systems. Photonic nanostructures are often employed in the single emitter regime for this purpose, but their applicability to widefield sensing with NV ensembles remains largely unexplored. Here we fabricate and characterize closely-packed arrays of diamond nanopillars, each hosting its own dense, near-surface ensemble of NV centres. We explore the optimal geometry for diamond nanopillars hosting NV ensembles and realise enhanced spin and photoluminescence properties which lead to increased measurement sensitivities (greater than a factor of 3) when compared to unpatterned surfaces. Utilising the increased measurement sensitivity, we image the mechanical stress tensor in each nanopillar across the arrays and show the fabrication process has negligible impact on in-built stress compared to the unpatterned surface. Our results demonstrate that photonic nanostructuring of the diamond surface is a viable strategy for increasing the sensitivity of ensemble-based widefield sensing and imaging.
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Nitrogen-vacancy (NV) centers in diamond have shown promise as inherently localized electric-field sensors, capable of detecting individual charges with nanometer resolution. Working with NV ensembles, we demonstrate that a detailed understanding of the internal electric field environment enables enhanced sensitivity in the detection of external electric fields. We follow this logic along two complementary paths. First, using excitation tuned near the NVs zero-phonon line, we perform optically detected magnetic resonance (ODMR) spectroscopy at cryogenic temperatures in order to precisely measure the NV centers excited-state susceptibility to electric fields. In doing so, we demonstrate that the characteristically observed contrast inversion arises from an interplay between spin-selective optical pumping and the NV centers local charge distribution. Second, motivated by this understanding, we propose and analyze a novel scheme for optically-enhanced electric-field sensing using NV ensembles; we estimate that our approach should enable order of magnitude improvements in the DC electric-field sensitivity.
We demonstrate magnetometry by detection of the spin state of high-density nitrogen-vacancy ensembles in diamond using optical absorption at 1042 nm. With this technique, measurement contrast, and collection efficiency can approach unity, leading to an increase in magnetic sensitivity compared to the more common method of collecting red fluorescence. Working at 75 K with a sensor with effective volume $50 times 50 times 300$ microns^3, we project photon shot-noise limited sensitivity of 5 pT in one second of acquisition and bandwidth from dc to a few megahertz. Operation in a gradiometer configuration yields a noise floor of 7 nTrms at ~110 Hz in one second of acquisition.
Powered by the mutual developments in instrumentation, materials andtheoretical descriptions, sensing and imaging capabilities of quantum emitters insolids have significantly increased in the past two decades. Quantum emitters insolids, whose properties resemble those of atoms and ions, provide alternative waysto probing natural and artificial nanoscopic systems with minimum disturbance andultimate spatial resolution. Among those emerging quantum emitters, the nitrogen-vacancy (NV) color center in diamond is an outstanding example due to its intrinsicproperties at room temperature (highly-luminescent, photo-stable, biocompatible,highly-coherent spin states). This review article summarizes recent advances andachievements in using NV centers within nano- and single crystal diamonds in sensingand imaging. We also highlight prevalent challenges and material aspects for differenttypes of diamond and outline the main parameters to consider when using color centersas sensors. As a novel sensing resource, we highlight the properties of NV centersas light emitting electrical dipoles and their coupling to other nanoscale dipoles e.g.graphene.
We present systematic measurements of longitudinal relaxation rates ($1/T_1$) of spin polarization in the ground state of the nitrogen-vacancy (NV$^-$) color center in synthetic diamond as a function of NV$^-$ concentration and magnetic field $B$. NV$^-$ centers were created by irradiating a Type 1b single-crystal diamond along the [100] axis with 200 keV electrons from a transmission electron microscope with varying doses to achieve spots of different NV$^-$ center concentrations. Values of ($1/T_1$) were measured for each spot as a function of $B$.
Negatively charged nitrogen-vacancy centres in diamond are promising quantum magnetic field sensors. Laser threshold magnetometry has been a theoretical approach for the improvement of NV-centre ensemble sensitivity via increased signal strength and magnetic field contrast. In this work we experimentally demonstrate laser threshold magnetometry. We use a macroscopic high-finesse laser cavity containing a highly NV-doped and low absorbing diamond gain medium that is pumped at 532nm and resonantly seeded at 710nm. This enables amplification of the signal power by stimulated emission of 64%. We show the magnetic-field dependency of the amplification and thus, demonstrate magnetic-field dependent stimulated emission from an NV-centre ensemble. This emission shows a record contrast of 33% and a maximum output power in the mW regime. These advantages of coherent read-out of NV-centres pave the way for novel cavity and laser applications of quantum defects as well as diamond NV magnetic field sensors with significantly improved sensitivity for the health, research and mining sectors.
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