Quantum sensing of low-frequency fields

A high sensitivity and resolution are important advantages of quantum sensing for many applications, such as nuclear magnetic resonance (NMR) of molecules. Fourier-based algorithms have been investigated for measuring such NMR signals [1]. However, their frequency-range is limited: it works at high frequencies only (over ~1 kHz) since dynamical decoupling sequences are applied. On the other hand, studying low-frequency signals is important for chemical structure analysis and for searching new particles beyond the standard model [2]. Previously, optically detected magnetic resonance techniques were used to detect low-frequency signals, though they are not as sensitive as coherence-based methods [3]. Here, we explore and demonstrate a fitting-based algorithm to measure low-frequency fields with an over two orders of magnitude higher sensitivity, which is frequency independent in the low-frequency range [4]. Moreover, we study the possibility to measure at ultra-low fields, working towards low-field NMR. Finally, as proof-of-concept measurement, we detect example low-frequency NMR signals, giving a narrow line width for the free nuclear precession of water of 1.6 Hz.

[1] Nature 555, 351-354 (2018).

[2] arXiv:2302.12756 (2023).

[3] Phys. Rev. B 84, 195204 (2011).

[4] Phys. Rev. Appl. 18, 034058 (2022).