Global NMR Discussion Meetings

Zero to Ultra Low Field

  • Real-time zero-field magnetometry using a single NV center coupled to a first-shell 13C nuclear spin in diamond

    Pralekh Dubey (IISER Bhopal, India)

    LinkedIn: Pralekh Dubey

    Abstract: Nitrogen-vacancy (NV) centers in diamond are robust and versatile solid-state defects that serve as optically addressable spin qubits under ambient conditions. When coupled to nearby first-shell 13C nuclear spins, they form a hybrid electron-nuclear spin system with rich hyperfine structure, which can also serve as a quantum register for NMR, quantum information processing and sensing applications 1. Here, we explore this coupled system in the context of zero-field quantum sensing 2. We demonstrate real-time zero-field magnetometry using first-shell 13C-coupled single NV centers in diamond. The strong hyperfine interaction (~130MHz) 3 with the proximal 13C spin lifts the degeneracy of the NV spin transitions and provides an intrinsic bias in the absence of an external magnetic field 4,5. Selective addressing and tracking of individual transitions under zero-field conditions, allows time-varying magnetic fields (up to few Hz) to be monitored in real time. This work highlights how coupled NV-13C spin systems are valuable for real-time zero-field magnetometry, with possible extension to other solid-state systems.

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  • Exploring spin dynamics of liquid sample in ZULF NMR

    Mansi Tarani (Tata Institute of Fundamental Research Hyderabad, India)

    LinkedIn: Mansi Tarani

    Abstract: NMR is a powerful technique to investigate the structure and dynamics of molecules by manipulating nuclear spins. In the zero- to ultra-low-field (ZULF) regime (≤ few tens of μT), spin dynamics are dominated by spin-spin interactions rather than Zeeman interactions. In this regime, the Larmor frequency lies in the range from Hz to a few kHz; consequently, spins can be manipulated using external DC magnetic fields. As pickup coils are less sensitive to such low frequencies, detection is done using highly sensitive magnetometers. In this work, we use commercial magnetometer (QuSpin) along with a home-built atomic magnetometer (AM) (sensitivity ~ 1pT/√Hz, dynamic range ~ 20μT, bandwidth ~ 24kHz and response time ~ 200 μs), which enables detection of system response in the range of a few kHz with short transverse relaxation times. We explored NMR spectra of different liquid samples over a magnetic field range from 50nT to 10μT. As the magnetic field strength increased, the spin coherence time decreased due to increasing field inhomogeneity across the sample. To refocus the signal, we used CPMG pulse sequence and further enhanced SNR by the introduction of phase cycling, which eliminated the correlated noise across successive scans. We also investigated the spin-spin (T2) and spin–lattice (T1) relaxation times. We observed an increase in (T2) time compared to high-field NMR because various dephasing effects become weaker in this regime. This work demonstrates the potential of ZULF NMR for precision relaxation studies and provides a pathway toward portable, low-cost spectroscopic and sensing applications.

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  • Toward Understanding of Nuclear Spin Relaxation at Zero-to-Ultralow Fields

    Chengtong Zhang (New York University, United States)

    Abstract: NMR experiments can interrogate a broad spectrum of molecular tumbling regimes and can accurately measure interatomic distances in solution with sub-nanometer resolution. Relaxation rates of nuclear spin polarization can unravel many dynamical and structural aspects of biomolecules in their native form. The high field relaxometry/dispersion techniques are widely used to monitor protein folding, molecular size, intermolecular interactions etc. However, little effort was devoted to extracting molecular information from relaxation rates at zero-to-ultralow-field (ZULF) mainly due to poor SNR and intricate spin dynamics. We develop the theoretical framework to understand relaxation rates measured in a ZULF-NMR setup with detection using optical-atomic magnetometers. In regimes where the scalar coupling constants and differences in Larmor frequencies of heteronuclear systems AX(N-1) have similar magnitudes, the spectrum reaches its maximum complexity with 2^N peaks. Populations and coherences’ lifetime measurements will greatly depend on the choice of monitored peaks’ decay. This multifaceted analysis of the same relaxation interaction can lead to a more accurate and robust determination of its strength and correlation time leading to new strategies for simultaneous extraction of structural and dynamical. We highlight how several factors impact the observed rates, such as (i) the shuttling profile from the (pre)polarizing magnet to the detection region, (ii) the measurement field, (iii) the detection method (single- or dual-channel) and even (iv) the nutation angle induced by the detection pulse. Our findings are compared to experimental relaxation rates measured for two [13C]-labelled molecules, showing how structural constraints and rotational tumbling can be inferred from ZULF relaxometry studies.

    1. Blake Wilson Avatar
      Blake Wilson

      Hello Chengtong, great presentation. This is very interesting with all of the different rates contributing. Can you comment on the origin of the two relaxation components (slow and fast)?

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      1. Chengtong Zhang Avatar
        Chengtong Zhang

        Hi Blake! Thank you for your question! The two relaxation components were derived from a Bi exponential decay model by fitting the amplitude of the signal through storage time(The time we wait for polarization). And the model of the Bi exponential decay was from the population evolution, via the dipole-dipole interaction in the relaxation mechanism.

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  • Ultralow-field nuclear magnetic resonance for direct nondestructive observation of electrolyte composition in batteries

    Roman Picazo-Frutos – @PicazoFrutosN

    Rechargeable batteries represent a key transformative technology for electric vehicles, portable electronics, and renewable energy. Despite enormous developments in battery research, there are few nondestructive diagnostic techniques compatible with realistic commercial-type cell enclosures. Many battery failures result from the loss or chemical degradation of electrolyte. Here we show measurements that allow quantification of electrolyte amount, composition, and potentially degradation, through battery enclosures. Instrumentation and techniques developed in the context of zero-to-ultralow-field nuclear magnetic resonance (ZULF NMR) with optically pumped atomic magnetometers as the detection elements are used for this study. In contrast to conventional NMR methodology, the reduced background magnetic fields employed here make even potentially thick stacks of battery housing and electrodes transparent to the lower-frequency electromagnetic fields involved. Both the solvent and lithium-salt components of the chemical signature can be quantified, as the results described herein demonstrate.

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