Longitudinal Pulsed Dynamic Nuclear Polarization Transfer via Periodic Optimal Control

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Quantum Control

Background:

• Pulsed dynamic nuclear polarization (DNP) enhances Nuclear Magnetic Resonance (NMR) sensitivity by transferring electron polarization to nuclear spins.
• Current pulsed DNP methods often rely on transverse spin-locking and Hartmann-Hahn matching, which can be limited by excitation pulse imperfections.
• Continuous-wave DNP is the prevailing method, but pulsed DNP offers potential for improved performance and flexibility.

Purpose of the Study:

• To develop a new family of broadband pulsed DNP pulse sequences to overcome the limitations of existing methods.
• To achieve efficient longitudinal polarization transfer, mitigating challenges associated with excitation pulses in DNP.
• To enhance NMR sensitivity through advanced DNP techniques.

Main Methods:

• Application of optimal control theory and effective Hamiltonian theory to design novel DNP pulse sequences.
• Development of the Longitudinally Optimized with Overarching Periodicity (LOOP) pulse sequences.
• Characterization of sequence performance under microwave field inhomogeneity and at a specific magnetic field (0.35 T).

Main Results:

• The LOOP sequences enable robust single-spin effective z rotations, demonstrating effective longitudinal polarization transfer.
• These sequences exhibit significant compensation for microwave field inhomogeneity.
• Achieved DNP transfer bandwidths exceeding 100 MHz with a modest peak microwave field amplitude of 32 MHz.

Conclusions:

• The LOOP pulse sequences represent a significant advancement in pulsed DNP, offering enhanced performance and robustness.
• These sequences effectively address the challenge of excitation pulse limitations in DNP applications.
• The demonstrated broadband capability and efficiency open new avenues for high-sensitivity NMR spectroscopy.