Detection of ultra-low field NMR signal with a commercial QuSpin single-beam atomic magnetometer

We experimentally demonstrate the nuclear magnetic resonance (NMR) detection at 1.9 kHz using a detection system comprised of a high-sensitivity single-beam atomic magnetometer and a flux transformer. The single-beam atomic magnetometer has been commercialized by QuSpin for typical operation at low frequencies below 200 Hz with a bandwidth of 135 Hz [1]. However, this magnetometer operation can be extended to much higher frequencies about 2 kHz by applying optimal-bias magnetic fields. The sensitivity of the detection system with a demonstrated signal-to-noise ratio of about 50 for a 20 ml water sample, even without magnetic field shimming, is quite competitive with that in other ultra-low field NMR detection systems, such as the Magritek Terranova system or the system based on our home-built atomic magnetometer installed inside a magnetically shielded room [2]. This ultra-low field NMR approach can be applied to Earth-field NMR detection and imaging. We estimate that the detection system with a modified flux transformer can be sensitive to underground-water detection at depth of 1 meter and deeper, and to field mapping applications.