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Despite its versatility and high chemical specificity, conventional nuclear magnetic resonance (NMR) spectroscopy is limited in measurement throughput due to the need for high-homogeneity magnetic fields, necessitating sequential sample analysis, and expensive devices. Here, we propose a multichannel NMR device that addresses these limitations by leveraging the zero-to ultralow-field (ZULF) regime, where simultaneous detection of multiple samples is carried out via an array of compact optically pumped magnetometers (OPMs). A magnetic field is used only for prepolarization, permitting the use of large-bore, high-field, inhomogeneous magnets that can accommodate multiple samples concurrently. Through systematic improvements, we demonstrate sensitive, high-resolution ZULF NMR spectroscopy with sensitivity comparable to benchtop 13C NMR systems. The spectroscopy remains robust without the need for field shimming for periods on the order of weeks. We show the detection of ZULF NMR signals from organic molecules without isotopic enrichment, and demonstrate the parallelized detection of three distinct samples simultaneously as a proof-of-concept, with the ability to scale further to over 100 channels at a cost comparable to traditional liquid state NMR systems. This work sets the stage for using multichannel “NMR camera” devices for inline reaction monitoring, robotic chemistry, quality control, and high-throughput assays. 

Quantum sensors have notably advanced high-sensitivity magnetic field detection. Here, we report quantum sensors constructed from polarized spin-triplet electrons in photoexcited organic chromophores, specifically focusing on pentacene-doped para-terphenyl $(\approx 0.1\%)$. We demonstrate essential quantum sensing properties at room temperature (RT): optically generated electronic polarization and state-dependent fluorescence contrast by leveraging differential pumping and relaxation rates between triplet and ground states. We measure high optically detected magnetic resonance contrast $\approx 16.8\%$of the triplet states at RT, along with long coherence times under spin echo and Carr-Purcell-Meiboom-Gill (CPMG) sequences, $T_2=2.7\mu \mathrm{s}$and $T_2^{\text{DD}}=18.4\mu \mathrm{s}$, respectively, limited only by the triplet lifetimes. The material offers several advantages for quantum sensing, including the ability to grow large (cm scale) crystals at low cost, absence of paramagnetic impurities, and electronic diamagnetism when not optically illuminated. Utilizing pentacene as a representative of a broader class of spin triplet- polarizable organic molecules, this paper highlights the potential for quantum sensing in chemical systems. 

High-temperature annealing is a promising but still mainly unexplored method for enhancing spin properties of negatively charged nitrogen-vacancy (NV) centers in diamond particles. After high-energy irradiation, the formation of NV centers in diamond particles is typically accomplished via annealing at temperatures in the range of 800–900 °C for 1–2 h to promote vacancy diffusion. Here, we investigate the effects of conventional annealing (900 °C for 2 h) against annealing at a much higher temperature of 1600 °C for the same annealing duration for particles ranging in size from 100 nm to 15 μm using electron paramagnetic resonance and optical characterization. At this high temperature, the vacancy-assisted diffusion of nitrogen can occur. Previously, the annealing of diamond particles at this temperature was performed over short time scales because of concerns of particle graphitization. Our results demonstrate that particles that survive this prolonged 1600 °C annealing show increased NV T1 and T2 electron spin relaxation times in 1 and 15 μm particles, due to the removal of fast relaxing spins. Additionally, this high-temperature annealing also boosts magnetically induced fluorescence contrast of NV centers for particle sizes ranging from 100 nm to 15 μm. At the same time, the content of NV centers is decreased fewfold and reaches a level of <0.5 ppm. The results provide guidance for future studies and the optimization of high-temperature annealing of fluorescent diamond particles for applications relying on the spin properties of NV centers in the host crystals.