Quantum Magnetic J-Oscillators
Dr. Danila Barskiy (Helmholtz Institute Mainz)

We introduce quantum magnetic J-oscillators that operate at zero magnetic field by exploiting nuclear spin-spin J-coupling transitions in molecules. This is achieved by coupling in situ hyperpolarized samples to a programmable digital feedback system that digitizes, delays, and amplifies the sample-generated magnetic field before feeding it back to the sample. Due to the insensitivity of the J-couplings to magnetic field drifts, we achieved coherent J-oscillations lasting over 3000 s, with a linewidth of 337 μHz limited primarily by acquisition time, reaching the Cramér-Rao lower bound in estimating error in frequency measurement [1]. The ability to control the feedback delay and gain enabled us to resolve overlapping resonances, making possible on-demand spectral editing. Application of quantum oscillators was demonstrated on a diverse range of molecules (nitriles, heterocycles, organic acids). The J-oscillators produce highly resolved, sharp spectra, reveal hidden transitions, and may allow distinction of complex mixtures that conventional zero-field NMR [2] cannot resolve. As a result, this approach can expand the scope of zero-field NMR for analytical chemistry, biomolecular characterization, and fundamental physics.

[1]. S. Fleischer, S. Lehmkuhl, L. Lohmann, S. Appelt, Approaching the Ultimate Limit in Measurement Precision with RASER NMR. Appl. Magn. Reson. 54 (11), 1241–1270 (2023).
[2]. D. A. Barskiy, et al., Zero- to Ultralow-field Nuclear Magnetic Resonance. Prog. Nucl. Magn. Reson. Spectrosc. (2025).