High Resolution Magnetic Resonance Spectroscopy Using Solid-State Spins (1705.08887v2)

Abstract: We demonstrate a synchronized readout (SR) technique for spectrally selective detection of oscillating magnetic fields with sub-millihertz resolution, using coherent manipulation of solid state spins. The SR technique is implemented in a sensitive magnetometer (~50 picotesla/Hz^1/2) based on nitrogen vacancy (NV) centers in diamond, and used to detect nuclear magnetic resonance (NMR) signals from liquid-state samples. We obtain NMR spectral resolution ~3 Hz, which is nearly two orders of magnitude narrower than previously demonstrated with NV based techniques, using a sample volume of ~1 picoliter. This is the first application of NV-detected NMR to sense Boltzmann-polarized nuclear spin magnetization, and the first to observe chemical shifts and J-couplings.

• The paper introduces a synchronized readout technique using NV centers in diamond, achieving sub-mHz resolution in NMR spectroscopy.
• The method reduces NMR spectral linewidth to approximately 3 Hz and detects chemical shifts and J-couplings in few-picoliter liquid samples.
• The approach paves the way for nanoscale and single-cell NMR applications by overcoming limitations in spin lifetime and sample polarization.

High Resolution Nuclear Magnetic Resonance Spectroscopy Using Solid-State Spins

The paper presented by Bucher et al. introduces an advanced methodology in the field of nuclear magnetic resonance (NMR) spectroscopy by employing a synchronized readout (SR) technique for spectrally selective detection of oscillating magnetic fields, harnessing the coherent manipulation of solid-state spins, specifically nitrogen vacancy (NV) centers in diamond. This approach significantly enhances the spectral resolution capabilities of NV-based NMR techniques, achieving sub-millihertz resolution and addressing prevalent limitations in the field.

Key Methodology and Implementation

The authors have demonstrated a potent SR technique as an integral part of a sensitive magnetometer (~50 picotesla/Hz$^{1/2}$) using NV centers, substantially decreasing the NMR spectral linewidth to approximately 3 Hz — a notable improvement by nearly two orders of magnitude relative to preceding NV-based techniques. The paper successfully captures nuclear magnetic resonance signals from liquid-state samples in minimal volume (~1 picoliter), marking this as the first instance of NV-detected NMR observing Boltzmann-polarized nuclear spin magnetization while detecting chemical shifts and J-couplings.

The experimental setup leverages a concatenated sequence of NV magnetometry interspersed with projective NV spin state readouts aligned with an external clock, deviating from traditional NV detection protocols which depend on statistical fluctuations. This precision allows the NV fluorescence intensity to offer insight into magnetic field variations, with coherent synchronization ensuring magnetic signals produce a discernible frequency shift over successive readout iterations. This technique mitigates previous challenges associated with short NV spin state lifetimes and fickle sample polarization levels in nanoscale samples.

Experimental Results and Observations

In trials using both a single NV center and an NV ensemble sensor, the paper consistently reports a spectral resolution of 5.2 mHz (full-width half-maximum, FWHM) from an antenna-generated signal, advancing to an impressive 0.4 mHz without averaging when extending the detection period. Applying this methodology to substances like glycerol and water confirmed the enhanced spectral resolution, capable of resolving chemical shifts and molecular structures heretofore unseen in NV-based NMR.

Furthermore, experiments on few-picoliter samples of trimethyl phosphate and xylene revealed the capability to observe distinct peak splittings corresponding to J-couplings and chemical shifts, demonstrating the potential for precise molecular structure characterization in low-volume samples.

Implications and Future Directions

The research sets a crucial precedent for utilizing solid-state spin sensors in NMR spectroscopy beyond previously accessible boundaries. This advancement potentially opens pathways for single-cell NMR spectroscopy and small molecule analysis at the picoliter scale, significantly expanding the scope of applications in biochemical and materials science domains.

The possibility of increasing spectral resolution through enhanced external magnetic fields, up to ~1 tesla, reinforces the potential to breach further performance barriers while indicating a shift towards macroscopic NV ensemble sensors for high-throughput, concentration-limited sample analysis in future applications.

The paper outlines technical challenges in SR protocols primarily concerning the weak coupling requirement and spin state readout fidelity, especially for single-NV sensor configurations. However, the adoption of advanced NV readout techniques such as charge-state detection and leveraging diamond NV orientation improvements may alleviate existing limitations, paving the way for more refined and sensitive NMR sensing tools in forthcoming endeavors.

In conclusion, the demonstrated advances underscore the strength of the synchronized readout methodology among NV-based NMR techniques, establishing new avenues for high-resolution spectroscopy, particularly in small-volume and potentially single-cell investigations, with promising enhancements forthcoming through continued methodological and material advancements in diamond NV center technology.