Nuclear magnetic resonance (NMR) spectroscopy is widely used in fields ranging from chemistry and materials science to neuroscience. Nanoscale NMR spectroscopy using nitrogen-vacancy (NV) centers in diamond has emerged as a promising platform due to an unprecedented sensitivity down to the single spin level. At the nanoscale, high nuclear spin polarization through spin fluctuations (statistical polarization) far outweighs thermal polarization. However, until now efficient NMR detection using coherent averaging techniques could not be applied to the detection of statistical polarization, leading to long measurement times. Here we present two protocols to enable coherent averaging of stochastic oscillatory signals through rectification. We demonstrate these protocols on an artificial radio frequency signal detected with a single NV center at 2.7 T. The signal-to-noise scaling with number of measurements N increases from N^{0.5} to N^{1}, improving the measurement time significantly. The relevance of rectification for the detection of statistically polarized nuclear spins using ensembles of NV centers is outlined, paving the way for efficient nanoscale NMR spectroscopy.
Nuclear magnetic resonance (NMR) spectroscopy is widely used in fields ranging from chemistry and materials science to neuroscience. Nanoscale NMR spectroscopy using nitrogen-vacancy (NV) centers in diamond has emerged as a promising platform due to an unprecedented sensitivity down to the single spin level. At the nanoscale, high nuclear spin polarization through spin fluctuations (statistical polarization) far outweighs thermal polarization. However, until now efficient NMR detection using coherent averaging techniques could not be applied to the detection of statistical polarization, leading to long measurement times. Here we present two protocols to enable coherent averaging of stochastic oscillatory signals through rectification. We demonstrate these protocols on an artificial radio frequency signal detected with a single NV center at 2.7 T. The signal-to-noise scaling with number of measurements N increases from N^{0.5} to N^{1}, improving the measurement time significantly. The relevance of rectification for the detection of statistically polarized nuclear spins using ensembles of NV centers is outlined, paving the way for efficient nanoscale NMR spectroscopy.
Nuclear magnetic resonance (NMR) spectroscopy is widely used in fields ranging from chemistry, materials science to neuroscience. Nanoscale NMR spectroscopy using Nitrogen-vacancy (NV) centers in diamond has emerged as a promising platform due to an unprecedented sensitivity down to the single spin level. At the nanoscale, high nuclear spin polarization through spin fluctuations (statistical polarization) far outweighs thermal polarization. However, until now efficient NMR detection using coherent averaging techniques could not be applied to the detection of statistical polarization, leading to long measurement times. Here we present two protocols to enable coherent averaging of statistically oscillating signals through rectification. We demonstrate these protocols on an artificial radiofrequency signal detected with a single NV center at 2.7 T. The signal-to-noise scaling with number of measurements 𝑁 increases from 𝑁0.5 to 𝑁1, improving the measurement time significantly. The relevance of rectification for the detection of statistically polarized nuclear spins using ensembles of NV centers is outlined, paving the way for efficient nanoscale NMR spectroscopy.
Nuclear magnetic resonance spectroscopy with solid-state spin sensors is a promising pathway for the detection of nuclear spins at the micro- and nanoscale. Although many nanoscale experiments rely on a single sensor spin for the detection of the signal, leveraging spin ensembles can enhance sensitivity, particularly in cases in which the signal merely originates from statistically polarized nuclear spins. In this Letter, we introduce multipoint correlation spectroscopy, which combines the advantages of two well-established methods-correlation spectroscopy and quantum heterodyne detection-to enable temporally efficient measurements of statistically polarized samples at the nanoscale with spin ensembles. We present a theoretical framework for this approach and demonstrate an experimental proof of concept with a nitrogen vacancy center in diamond. We achieve single hertz uncertainty in the estimated signal frequency, highlighting the potential applications of the technique for nanoscale nuclear magnetic resonance.
Spin defects in solids, such as the nitrogen-vacancy (NV) center in diamond, have emerged as a key tool for detecting nuclear spins at the nanoscale. While active nuclear spin control via radio-frequency (RF) irradiation is often unnecessary for standard spin-noise detection, it becomes essential for advanced protocols like multidimensional nanoscale NMR. In this work, we investigate nuclear spin control using correlation spectroscopy techniques. We demonstrate, both theoretically and experimentally, that the resulting nuclear spin dynamics depend critically on the initial RF phase and its orientation relative to the NV crystalline axis. Depending on these parameters, identical nuclear rotations can yield full, partial, or even vanishing contrast in the NV readout. These findings highlight a previously underappreciated aspect of spin manipulation in the spin-noise regime: the link between the phase and direction of the applied RF field and its direct impact on correlation-based experiments. Consequently, imperfect calibration of these parameters can lead to ambiguous signal contrasts and misinterpretation of the underlying nuclear spin dynamics. Our results provide deeper insight into nanoscale spin control and pave the way toward reliable multidimensional spin resonance experiments.
Quantum technologies are expected to significantly change our world in the next decades and the possible applications are diverse – ranging from quantum computation and encryption to metrology with unprecedented sensitivity. This thesis focuses on quantum sensing and imaging based on single nitrogen-vacancy (NV) centres in diamond to measure magnetic fields. Its electronic spin qualifies this point defect as a highly sensitive quantum sensor and its atomic size offers nanoscale spatial resolution. The simple optical initialisation and readout, together with the relatively long coherence time at ambient conditions, make NV centres promising candidates for biological applications and in particular for nuclear magnetic resonance (NMR) on the nanoscale. Recording the spectral information on the nanoscale allows to determine the structure of single or just a few molecules. However, the current main problems and challenges include insufficient spectral resolution, artificial signals and overall poor performance. In this thesis new spectroscopic techniques which tackle these issues are presented. First, it is shown that by randomisation of control pulse phases spurious harmonic signals can be suppressed, which otherwise complicate spectrum interpretation and can lead to false signal identification. At the same time the effects of pulse imperfections are mitigated. Furthermore, a protocol allowing to measure with a coherence independent spectral resolution is presented. It is demonstrated that linewidths below 1mHz are possible, which is an improvement of more than seven orders of magnitude compared to traditional methods. Due to its simple implementation, the protocol is relevant for many applications. Initially developed to measure signals oscillating up to several megahertz, it is further shown that modifications allow to extend the frequency range into the gigahertz domain. Finally, quantum frequency discrimination with the task to differentiate between two frequency distributions using a quantum sensor is analysed. An optimised protocol is introduced and the influences of different readout strategies are discussed with respect to the probability to make an incorrect decision. These findings are useful for diagnostic tests in NMR.
Nuclear magnetic resonance (NMR) spectroscopy provides unparalleled access to molecular structure and dynamics but is traditionally limited by weak signal strength, requiring large sample volumes and high magnetic fields. Here, we demonstrate nanoscale deuterium (2H) NMR spectroscopy using nitrogen vacancy (NV) centers in diamond, reproducing the characteristic quadrupolar powder line shapes that are present in the conventional bulk NMR spectra. By detecting statistical spin fluctuations from nanometer scale detection volumes, our approach delivers a sensitivity enhancement of six to eight orders of magnitude over inductive detection while operating at magnetic fields two orders of magnitude lower than those used in conventional NMR. Temperature dependent measurements of a deuterated polymer and molecular solid reveal distinct motional averaging and phase transitions with nanoscale sensitivity. Powder-like NV detected 2H NMR establishes a powerful tool for probing molecular dynamics on the nanoscale and, in the ultimate limit, at the single molecule level - capabilities beyond those of most existing spectroscopic techniques.
Abstract Quantum systems composed of solid-state electronic spins can be sensitive detectors of narrowband magnetic fields. A prominent example is the nitrogen-vacancy (NV) center in diamond, which has been employed for magnetic spectroscopy with high spatial and spectral resolution. However, NV-diamond spectroscopy protocols are typically based on dynamical decoupling sequences, which are limited to low-frequency signals (≲ 20 MHz) due to the technical requirements on microwave (MW) pulses used to manipulate NV electronic spins. In this work, we experimentally demonstrate a high-resolution magnetic spectroscopy protocol that integrates a quantum frequency mixing (QFM) effect in a dense NV ensemble with coherently averaged synchronized readout (CASR) to provide both a wide range of signal frequency detection and sub-Hz spectral resolution. We assess the sensitivity of this QFM-CASR protocol across a frequency range of 10 MHz to 4 GHz. By measuring the spectra of multi-frequency signals near 0.6, 2.4 and 4 GHz, we demonstrate sub-Hz spectral resolution with a nT-scale noise floor for the target signal, and precise phase measurement with error <1°. Compared to state-of-the-art NV-diamond techniques for narrowband magnetic spectroscopy, the QFM-CASR protocol greatly extends the detectable frequency range, enabling applications in high-frequency radio frequency (RF) and MW signal microscopy and analysis, as well as tesla-scale nuclear magnetic resonance (NMR) spectroscopy of small samples.