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We report on measurements of the photoluminescence properties of single nitrogen-vacancy centers in diamond at temperatures between 4 K and 300 K. We observe a strong reduction of the PL intensity and spin contrast between ca. 10 K and 100 K that recovers to high levels below and above. Further, we find a rich dependence on magnetic bias field and crystal strain. We develop a comprehensive model based on spin mixing and orbital hopping in the electronic excited state that quantitatively explains the observations. Beyond a more complete understanding of the excited-state dynamics, our work provides a novel approach for probing electron-phonon interactions and a predictive tool for optimizing experimental conditions for quantum applications.
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Quantum sensors based on spin defects in diamond have recently enabled detailed imaging of nanoscale magnetic patterns, such as chiral spin textures, two-dimensional ferromagnets, or superconducting vortices, based on a measurement of the static magnetic stray field. Here, we demonstrate a gradiometry technique that significantly enhances the measurement sensitivity of such static fields, leading to new opportunities in the imaging of weakly magnetic systems. Our method relies on the mechanical oscillation of a single nitrogen-vacancy center at the tip of a scanning diamond probe, which up-converts the local spatial gradients into ac magnetic fields enabling the use of sensitive ac quantum protocols. We show that gradiometry provides important advantages over static field imaging: (i) an order-of-magnitude better sensitivity, (ii) a more localized and sharper image, and (iii) a strong suppression of field drifts. We demonstrate the capabilities of gradiometry by imaging the nanotesla fields appearing above topographic defects and atomic steps in an antiferromagnet, direct currents in a graphene device, and para- and diamagnetic metals.
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Nuclear magnetic resonance imaging (MRI) at the atomic scale offers exciting prospects for determining the structure and function of individual molecules and proteins. Quantum defects in diamond have recently emerged as a promising platform towards reaching this goal, and allowed for the detection and localization of single nuclear spins under ambient conditions. Here, we present an efficient strategy for extending imaging to large nuclear spin clusters, fulfilling an important requirement towards a single-molecule MRI technique. Our method combines the concepts of weak quantum measurements, phase encoding and simulated annealing to detect three-dimensional positions from many nuclei in parallel. Detection is spatially selective, allowing us to probe nuclei at a chosen target radius while avoiding interference from strongly-coupled proximal nuclei. We demonstrate our strategy by imaging clusters containing more than 20 carbon-13 nuclear spins within a radius of 2.4 nm from single, near-surface nitrogen-vacancy centers at room temperature. The radius extrapolates to 5-6 nm for 1H. Beside taking an important step in nanoscale MRI, our experiment also provides an efficient tool for the characterization of large nuclear spin registers in the context of quantum simulators and quantum network nodes.
Assuntos
Diamante , Imageamento por Ressonância Magnética , Diamante/química , Imageamento por Ressonância Magnética/métodos , Nanotecnologia , Nitrogênio/química , ProteínasRESUMO
The active manipulation of nuclear spins with radio-frequency (RF) coils is at the heart of nuclear magnetic resonance (NMR) spectroscopy and spin-based quantum devices. Here, we present a miniature RF transmitter designed to generate strong RF pulses over a broad bandwidth, allowing for fast spin rotations on arbitrary nuclear species. Our design incorporates (i) a planar multilayer geometry that generates a large field of 4.35 mT per unit current, (ii) a 50 Ω transmission circuit with a broad excitation bandwidth of â¼20 MHz, and (iii) an optimized thermal management leading to minimal heating at the sample location. Using individual 13C nuclear spins in the vicinity of a diamond nitrogen-vacancy center as a test system, we demonstrate Rabi frequencies exceeding 70 kHz and nuclear π/2 rotations within 3.4 µs. The extrapolated values for 1H spins are about 240 kHz and 1 µs, respectively. Beyond enabling fast nuclear spin manipulations, our transmitter system is ideally suited for the incorporation of advanced pulse sequences into micro- and nanoscale NMR detectors operating at a low (<1 T) magnetic field.
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Magnetic resonance force microscopy (MRFM) is a scanning probe technique capable of detecting MRI signals from nanoscale sample volumes, providing a paradigm-changing potential for structural biology and medical research. Thus far, however, experiments have not reached sufficient spatial resolution for retrieving meaningful structural information from samples. In this work, we report MRFM imaging scans demonstrating a resolution of 0.9 nm and a localization precision of 0.6 nm in one dimension. Our progress is enabled by an improved spin excitation protocol furnishing us with sharp spatial control on the MRFM imaging slice, combined with overall advances in instrument stability. From a modeling of the slice function, we expect that our arrangement supports spatial resolutions down to 0.3 nm given sufficient signal-to-noise ratio. Our experiment demonstrates the feasibility of subnanometer MRI and realizes an important milestone toward the three-dimensional imaging of macromolecular structures.
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Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for analysing the structure and function of molecules, and for performing three-dimensional imaging of their spin densities. At the heart of NMR spectrometers is the detection of electromagnetic radiation, in the form of a free induction decay signal1, generated by nuclei precessing around an applied magnetic field. Whereas conventional NMR requires signals from 1012 or more nuclei, recent advances in sensitive magnetometry2,3 have dramatically lowered the required number of nuclei to a level where a few or even individual nuclear spins can be detected4-6. It is unclear whether continuous detection of the free induction decay can still be applied at the single-spin level, or whether quantum back-action (the effect that a detector has on the measurement itself) modifies or suppresses the NMR response. Here we report the tracking of single nuclear spin precession using periodic weak measurements7-9. Our experimental system consists of nuclear spins in diamond that are weakly interacting with the electronic spin of a nearby nitrogen vacancy centre, acting as an optically readable meter qubit. We observe and minimize two important effects of quantum back-action: measurement-induced decoherence10 and frequency synchronization with the sampling clock11,12. We use periodic weak measurements to demonstrate sensitive, high-resolution NMR spectroscopy of multiple nuclear spins with a priori unknown frequencies. Our method may provide a useful route to single-molecule NMR13,14 at atomic resolution.
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Nuclear magnetic resonance (NMR) spectroscopy is a powerful method for analyzing the chemical composition and molecular structure of materials. At the nanometer scale, NMR has the prospect of mapping the atomic-scale structure of individual molecules, provided a method that can sensitively detect single nuclei and measure inter-atomic distances. Here, we report on precise localization spectroscopy experiments of individual 13C nuclear spins near the central electronic sensor spin of a nitrogen-vacancy (NV) center in a diamond chip. By detecting the nuclear free precession signals in rapidly switchable external magnetic fields, we retrieve the three-dimensional spatial coordinates of the nuclear spins with sub-Angstrom resolution and for distances beyond 10 Å. We further show that the Fermi contact contribution can be constrained by measuring the nuclear g-factor enhancement. The presented method will be useful for mapping atomic positions in single molecules, an ambitious yet important goal of nanoscale nuclear magnetic resonance spectroscopy.
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Distance measurements via the dipolar interaction are fundamental to the application of nuclear magnetic resonance (NMR) to molecular structure determination, but they provide information on only the absolute distance r and polar angle θ between spins. In this Letter, we present a protocol to also retrieve the azimuth angle Ï. Our method relies on measuring the nuclear precession phase after the application of a control pulse with a calibrated external radio-frequency coil. We experimentally demonstrate three-dimensional positioning of individual ^{13}C nuclear spins in a diamond host crystal relative to the central electronic spin of a single nitrogen-vacancy center. The ability to pinpoint three-dimensional nuclear locations is central for realizing a nanoscale NMR technique that can image the structure of single molecules with atomic resolution.
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We present a "nanoladder" geometry that minimizes the mechanical dissipation of ultrasensitive cantilevers. A nanoladder cantilever consists of a lithographically patterned scaffold of rails and rungs with feature size â¼100 nm. Compared to a rectangular beam of the same dimensions, the mass and spring constant of a nanoladder are each reduced by roughly 2 orders of magnitude. We demonstrate a low force noise of 158-42+62 zN and 190-33+42 zN in a 1 Hz bandwidth for devices made from silicon and diamond, respectively, measured at temperatures between 100-150 mK. As opposed to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder cantilevers can be batch-fabricated using standard lithography, which is a critical factor for applications in scanning force microscopy.
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The production of nanowire materials, uniformly oriented along any arbitrarily chosen crystal orientation, is an important, yet unsolved, problem in material science. Here, we present a generalizable solution to this problem. The solution is based on the technique of glancing angle deposition combined with a rapid switching of the deposition direction between crystal symmetry positions. Using iron-cobalt as an example, we showcase the simplicity and capabilities of the process in one-step fabrications of ã100ã, ã110ã, ã111ã, ã210ã, ã310ã, ã320ã, and ã321ã-oriented nanowires, three-dimensional nanowire spirals, core-shell heterostructures, and axial hybrids. Our results provide a new capability for tailoring the properties of nanowires, and should be generalizable to any material that can be grown as a single-crystal biaxial film.
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The design and realization of a torque magnetometer is reported that reads the deflection of a membrane by optical interferometry. The compact instrument allows for low-temperature measurements of tiny crystals less than a microgram with a significant improvement in sensitivity, signal-to-noise ratio as well as data acquisition time compared with conventional magnetometry and offers an enormous potential for further improvements and future applications in different fields. Magnetic measurements on single-molecule magnets demonstrate the applicability of the membrane-based torque magnetometer.
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Quantum sensing takes advantage of well-controlled quantum systems for performing measurements with high sensitivity and precision. We have implemented a concept for quantum sensing with arbitrary frequency resolution, independent of the qubit probe and limited only by the stability of an external synchronization clock. Our concept makes use of quantum lock-in detection to continuously probe a signal of interest. Using the electronic spin of a single nitrogen-vacancy center in diamond, we demonstrate detection of oscillating magnetic fields with a frequency resolution of 70 microhertz over a megahertz bandwidth. The continuous sampling further guarantees an enhanced sensitivity, reaching a signal-to-noise ratio in excess of 104 for a 170-nanotesla test signal measured during a 1-hour interval. Our technique has applications in magnetic resonance spectroscopy, quantum simulation, and sensitive signal detection.
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Charge transport in nanostructures and thin films is fundamental to many phenomena and processes in science and technology, ranging from quantum effects and electronic correlations in mesoscopic physics, to integrated charge- or spin-based electronic circuits, to photoactive layers in energy research. Direct visualization of the charge flow in such structures is challenging due to their nanometer size and the itinerant nature of currents. In this work, we demonstrate noninvasive magnetic imaging of current density in two-dimensional conductor networks including metallic nanowires and carbon nanotubes. Our sensor is the electronic spin of a diamond nitrogen-vacancy center attached to a scanning tip and operated under ambient conditions. Using a differential measurement technique, we detect DC currents down to a few µA with a current density noise floor of â¼2 × 104 A/cm2. Reconstructed images have a spatial resolution of typically 50 nm, with a best-effort value of 22 nm. Current density imaging offers a new route for studying electronic transport and conductance variations in two-dimensional materials and devices, with many exciting applications in condensed matter physics and materials science.
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We investigate the application of amplitude-shaped control pulses for enhancing the time and frequency resolution of multipulse quantum sensing sequences. Using the electronic spin of a single nitrogen-vacancy center in diamond and up to 10 000 coherent microwave pulses with a cosine square envelope, we demonstrate 0.6-ps timing resolution for the interpulse delay. This represents a refinement by over 3 orders of magnitude compared to the 2-ns hardware sampling. We apply the method for the detection of external ac magnetic fields and nuclear magnetic resonance signals of ^{13}C spins with high spectral resolution. Our method is simple to implement and especially useful for quantum applications that require fast phase gates, many control pulses, and high fidelity.
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Sensitive detection of weak magnetic moments is an essential capability in many areas of nanoscale science and technology, including nanomagnetism, quantum readout of spins and nanoscale magnetic resonance imaging. Here we show that the write head of a commercial hard drive may enable significant advances in nanoscale spin detection. By approaching a sharp diamond tip to within 5 nm from a write pole and measuring the induced diamagnetic moment with a nanomechanical force transducer, we demonstrate a spin sensitivity of 0.032 µB Hz(-1/2), equivalent to 21 proton magnetic moments. The high sensitivity is enabled in part by the pole's strong magnetic gradient of up to 28 × 10(6) T m(-1) and in part by the absence of non-contact friction due to the extremely flat writer surface. In addition, we demonstrate quantitative imaging of the pole field with â¼10 nm spatial resolution. We foresee diverse applications for write heads in experimental condensed matter physics, especially in spintronics, ultrafast spin manipulation and mesoscopic physics.
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Chiral magnetic interactions induce complex spin textures including helical and conical spin spirals, as well as particle-like objects such as magnetic skyrmions and merons. These spin textures are the basis for innovative device paradigms and give rise to exotic topological phenomena, thus being of interest for both applied and fundamental sciences. Present key questions address the dynamics of the spin system and emergent topological defects. Here we analyse the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining magnetic force microscopy, single-spin magnetometry and Landau-Lifschitz-Gilbert simulations we show that the nanoscale dynamics are governed by the depinning and subsequent motion of magnetic edge dislocations. The motion of these topologically stable objects triggers perturbations that can propagate over mesoscopic length scales. The observation of stochastic instabilities in the micromagnetic structure provides insight to the spatio-temporal dynamics of itinerant helimagnets and topological defects, and discloses open challenges regarding their technological usage.
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We report on Fourier spectroscopy experiments performed with near-surface nitrogen-vacancy centers in a diamond chip. By detecting the free precession of nuclear spins rather than applying a multipulse quantum sensing protocol, we are able to unambiguously identify the NMR species devoid of harmonics. We further show that, by engineering different Hamiltonians during free precession, the hyperfine coupling parameters as well as the nuclear Larmor frequency can be selectively measured with up to five digits of precision. The protocols can be combined to demonstrate two-dimensional Fourier spectroscopy. Presented techniques will be useful for mapping nuclear coordinates in molecules deposited on diamond sensor chips, en route to imaging their atomic structure.
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We report the fabrication, integration, and assessment of sharp diamond tips for ultrasensitive force microscopy experiments. Two types of tips, corresponding to the upper and lower halves of a diamond nanowire, were fabricated by top-down plasma etching from a single-crystalline substrate. The lower, surface-attached halves can be directly integrated into lithographically defined nanostructures, like cantilevers. The upper, detachable halves result in diamond nanowires with a tunable diameter (50-500 nm) and lengths of a few microns. Tip radii were around 10 nm and tip apex angles around 15°. We demonstrate the integration of diamond nanowires for use as scanning tips onto ultrasensitive pendulum-style silicon cantilevers. We find the noncontact friction and frequency jitter to be exceptionally low, with no degradation in the intrinsic mechanical quality factor (Q ≈ 130,000) down to tip-to-surface distances of about 10 nm. Our results are an encouraging step toward further improvement of the sensitivity and resolution of force-detected magnetic resonance imaging.
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Extending magnetic resonance imaging to the atomic scale has been a long-standing aspiration, driven by the prospect of directly mapping atomic positions in molecules with three-dimensional spatial resolution. We report detection of individual, isolated proton spins by a nitrogen-vacancy (NV) center in a diamond chip covered by an inorganic salt. The single-proton identity was confirmed by the Zeeman effect and by a quantum coherent rotation of the weakly coupled nuclear spin. Using the hyperfine field of the NV center as an imaging gradient, we determined proton-NV distances of less than 1 nm.
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We present measurements of spin relaxation times (T1, T1ρ, T2) on very shallow (â²5 nm) nitrogen-vacancy centers in high-purity diamond single crystals. We find a reduction of spin relaxation times up to 30 times compared to bulk values, indicating the presence of ubiquitous magnetic impurities associated with the surface. Our measurements yield a density of 0.01-0.1µB/nm2 and a characteristic correlation time of 0.28(3) ns of surface states, with little variation between samples and chemical surface terminations. A low temperature measurement further confirms that fluctuations are thermally activated. The data support the atomistic picture where impurities are associated with the top carbon layers, and not with terminating surface atoms or adsorbate molecules. The low spin density implies that the presence of a single surface impurity is sufficient to cause spin relaxation of a shallow nitrogen-vacancy center.