Optically Detected Nuclear Magnetic Resonance Above and Far Below Earth's Magnetic Field

Sven Bodenstent

Dr. Morgan W. Mitchell Dr. Michael Tayler

“Atomic Quantum Optics” (ICFO)

Nuclear magnetic resonance (NMR) and its medical application, magnetic resonance imaging (MRI), are indispensable tools in modern medicine and research. However, these techniques rely on complex cryogenic superconducting magnets, making them expensive and often inaccessible, especially in resource-limited settings. This thesis presents an innovative approach that maintains high performance while eliminating the need for expensive infrastructure. The experimental platform developed during this research work has been successfully published under the name NMRduino and is now ready for commercial development, with the potential to democratize access to this crucial technology globally. This doctoral thesis describes the theory, simulations, experimental apparatus and measurements of nuclear spin dynamics using optically pumped magnetometers in unconventional magnetic regimes. This thesis is divided into four parts: magnetometry, nuclear magnetic resonance spectroscopy, nuclear relaxation scattering and nuclear spin control. The magnetometry section describes how, by integrating relaxation-free DC spin exchange techniques and RF magnetometers, a widely tunable magnetometer has been developed that offers a nearly flat response from DC to a few kHz with a sensitivity of less than 20 fT √Hz. In this range, it surpasses the capabilities of inductive detection methods and eliminates the need for cryogenic temperatures required in superconducting quantum interference devices (SQUIDs). In the next section, the magnetometer is used to perform nuclear magnetic resonance spectroscopy experiments on coupled nuclear spin systems. A comprehensive analysis is performed to find the magnetic field that gives the most accurate determination of the coupling constant J. It is shown that some systems in the ultra-low field regime offer advantages when compared to zero and high field regimes. A key factor in choosing the magnetic field is the strong dependence of the nuclear spin relaxation on the field. This dependence is explored in the third part of this thesis in the unconventional range of ultra-low fields, with a discussion of long-lived persistent coherences and the impact of extended correlations on molecular dynamics. This study is performed experimentally by adapting the established method of fast field cycling to ultra-low fields and combining it with optical detection. The final part of this thesis focuses on improving the manipulation of nuclear spin dynamics by advanced methods that ensure selective, efficient, accurate and error-proof spin control. Ultra-low fields have unique attributes that make even basic techniques such as spin-selective resonant pulses difficult to implement. To address this, new concepts have been developed that allow effective spin control in the ultra-low field range similar to or even better than their high-field counterparts. The effectiveness of these improved pulse sequences is demonstrated with dynamic decoupling, polarimetry, and spectral filtering experiments.

Expected Impact - Beyond Imaging While medical imaging represents a primary application, our NMR technology's potential extends far beyond clinical diagnoses, offering transformative capabilities across multiple sectors: Chemical Analysis and Quality Control  Real-time process monitoring in industry settings without requiring complex infrastructure  Quality control in pharmaceutical manufacturing, enabling on-line analysis of drug formulations  Environmental monitoring, including water quality assessment and pollutant detection  Food industry applications for composition analysis and authenticity verification Biological Research  Non-invasive monitoring of cellular processes and metabolic activities  Integration with microfluidic devices for laboratory chip applications  Real-time analysis of tissue cultures and microphysiological systems  Support for bioengineering research through compact, accessible NMR capabilities Industrial Applications  Process control in chemical manufacturing  Quality assurance in petroleum and polymer industries  Materials science research and development  Portable field testing for geological surveys  Battery operation enables true portability and operation in remote locations Advanced Research Applications  Fundamental physics research exploring quantum phenomena  Development of new hyperpolarization techniques  Investigation of molecular dynamics at ultralow fields  Novel spectroscopic methods for complex molecular systems The present project addresses unsolved problems that widen the scope of NMR within and beyond the clinical market. The long-term goal is to enable high-quality magnetic resonance applications without strong fields, potentially benefiting adjacent sectors of tissue-culture, microphysiology, bioengineering, and chip-based fluidics. Through continuous development and community-driven innovation, we anticipate expanding the platform's capabilities to meet emerging challenges across these diverse fields.

Nuclear Magnetic Resonance (NMR); Magnetic Resonance Imaging (MRI); Cryogenic Superconducting Magnets; Expensive Infrastructure; High Performance; Experimental Platform; NMRduino; Commercial Development; Democratize Access; Crucial Technology; Doctoral Thesis; Theory; Simulations; Experimental Apparatus; Measurements; Nuclear Spin Dynamics; Optically Pumped Magnetometers; Unconventional Magnetic Regimes; Magnetometry; Nuclear Magnetic Resonance Spectroscopy; Nuclear Relaxation Scattering; Nuclear Spin Control; Relaxation-free DC Spin Exchange Techniques; RF Magnetometers; Tunable Magnetometer; Flat Response; Sensitivity; Inductive Detection Methods; Cryogenic Temperatures; Superconducting Quantum Interference Devices (SQUIDs); Coupled Nuclear Spin Systems; Magnetic Field; Coupling Constant J; Ultra-Low Field (ULF); Zero Field; High Field; Nuclear Spin Relaxation; Long-lived Persistent Coherences; Extended Correlations; Molecular Dynamics; Fast Field Cycling; Optical Detection; Manipulation; Advanced Methods; Spin-selective Resonant Pulses; New Concepts; Effective Spin Control; Improved Pulse Sequences; Dynamic Decoupling; Polarimetry; Spectral Filtering