Inductive-detection electron-spin resonance spectroscopy with 65 spins/√Hz sensitivity

We report electron spin resonance spectroscopy measurements performed at millikelvin temperatures in a custom-built spectrometer comprising a superconducting micro-resonator at 7 GHz and a Josephson parametric amplifier. Owing to the small ( similar to 10(-12)lambda(3)) magnetic resonator mode volume and to the low noise of the parametric amplifier, the spectrometer's single shot sensitivity reaches 260 +/- 40 spins/echo translating into 65 +/- 10 spins/root Hz for repeated acquisition. Published by AIP Publishing.