Integrated diamond quantum spectrometer for high-resolution picoliter nuclear magnetic resonance (NMR) under ambient magnetic noise.

Nitrogen-vacancy (NV) centers in diamond enable Nuclear Magnetic Resonance (NMR) spectroscopy from picoliter-scale samples, providing a route toward volume-limited magnetic resonance measurements. However, achieving high spectral resolution in a compact integrated spectrometer remains challenging, particularly under ambient magnetic noise. Here, we present an integrated NV-NMR spectrometer based on a compact multilayer architecture that combines a diamond sensor, an ultrathin Printed Circuit Board antenna, a sealed liquid-sample chamber, and a custom permanent magnet. In this sealed-chamber configuration, the spectrometer operates with an estimated detection volume on the order of ten picoliters, achieves a magnetic sensitivity of 27 pT/Hz, and uses hyperpolarization to improve NMR signal detectability. The system further incorporates a dual-stabilization scheme based on asynchronous fluxgate monitoring and synchronous optically detected magnetic resonance drift tracking, enabling high-resolution operation under ambient field-induced proton-frequency shifts of up to ±40 Hz. Under ambient conditions, without heavy magnetic shielding or strict temperature control, the spectrometer achieves a proton NMR linewidth of 2.34 ± 0.05 Hz, corresponding to 0.450.01 ppm. These results establish a compact integrated architecture for high-resolution picoliter NMR under nonideal laboratory magnetic environments.