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Signal reception of nuclear magnetic resonance (NMR) usually relies on electrical amplification of the electromotive force caused by nuclear induction. Here, we report up-conversion of a radio-frequency NMR signal to an optical regime using a high-stress silicon nitride membrane that interfaces the electrical detection circuit and an optical cavity through the electro-mechanical and the opto-mechanical couplings. This enables optical NMR detection without sacrificing the versatility of the traditional nuclear induction approach. While the signal-to-noise ratio is currently limited by the Brownian motion of the membrane as well as additional technical noise, we find it can exceed that of the conventional electrical schemes by increasing the electro-mechanical coupling strength. The electro-mechano-optical NMR detection presented here opens the possibility of mechanical parametric amplification of NMR signals. Moreover, it can potentially be combined with the laser cooling technique applied to nuclear spins.
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Nuclear magnetic resonance (NMR) diffusion measurements are widely used to derive parameters indirectly related to the microstructure of biological tissues and porous media. However, a direct imaging of cell or pore shapes and sizes would be of high interest. For a long time, determining pore shapes by NMR diffusion acquisitions seemed impossible, because the necessary phase information could not be preserved. Here we demonstrate experimentally using the measurement technique which we have recently proposed theoretically that the shape of arbitrary closed pores can be imaged by diffusion acquisitions, which yield the phase information. For this purpose, we use hyperpolarized xenon gas in well-defined geometries. The signal can be collected from the whole sample which mainly eliminates the problem of vanishing signal at increasing resolution of conventional NMR imaging. This could be used to non-invasively gain structural information inaccessible so far such as pore or cell shapes, cell density or axon integrity.
We demonstrate nuclear magnetic resonance (NMR) spectroscopy of picoliter-volume solutions with a nanostructured diamond chip. Using optical interferometric lithography, diamond surfaces were nanostructured with dense, high-aspect-ratio nanogratings, enhancing the surface area by more than a factor of 15 over mm^2 regions of the chip. The nanograting sidewalls were doped with nitrogen-vacancy (NV) centers so that more than 10 million NV centers in a (25 micrometer)^2 laser spot are located close enough to the diamond surface (5 nm) to detect the NMR spectrum of 1 pL of fluid lying within adjacent nanograting grooves. The platform was used to perform 1H and 19F NMR spectroscopy at room temperature in magnetic fields below 50 mT. Using a solution of CsF in glycerol, we demonstrate that 4 +/- 2 x 10^12 19F spins in a 1 pL volume, can be detected with a signal-to-noise ratio of 3 in 1 s integration. This represents nearly two orders of magnitude improvement in concentration sensitivity over previous NV and picoliter NMR studies.
We describe a method based on precision magnetometry that can extend the search for axion-mediated spin-dependent forces by several orders of magnitude. By combining techniques used in nuclear magnetic resonance and short-distance tests of gravity, our approach can substantially improve upon current experimental limits set by astrophysics, and probe deep into the theoretically interesting regime for the Peccei-Quinn (PQ) axion. Our method is sensitive to PQ axion decay constants between 10^9 and 10^12 GeV or axion masses between 10^-6 and 10^-3 eV, independent of the cosmic axion abundance.
As a complementary analysis tool to conventional high-field NMR, zero- to ultralow-field (ZULF) NMR detects nuclear magnetization signals in the sub-microtesla regime. Spin-exchange relaxation-free (SERF) atomic magnetometers provide a new generation of sensitive detector for ZULF NMR. Due to the features such as low-cost, high-resolution and potability, ZULF NMR has recently attracted considerable attention in chemistry, biology, medicine, and tests of fundamental physics. This review describes the basic principles, methodology and recent experimental and theoretical development of ZULF NMR, as well as its applications in spectroscopy, quantum control, imaging, NMR-based quantum devices, and tests of fundamental physics. The future prospects of ZULF NMR are also discussed.
Ultralow-field nuclear magnetic resonance (NMR) provides a new regime for many applications ranging from materials science to fundamental physics. However, the experimentally observed spectra show asymmetric amplitudes, differing greatly from those predicted by the standard theory. Its physical origin remains unclear, as well as how to suppress it. Here we provide a comprehensive model to explain the asymmetric spectral amplitudes, further observe more unprecedented asymmetric spectroscopy and find a way to eliminate it. Moreover, contrary to the traditional idea that asymmetric phenomena were considered as a nuisance, we show that more information can be gained from the asymmetric spectroscopy, e.g., the light shift of atomic vapors and the sign of Land$acute{textrm{e}}$ $g$ factor of NMR systems.
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