Inductive-detection electron-spin resonance spectroscopy with $65$spins$/\sqrt{\text{Hz}}$ sensitivity

Abstract

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 $\sim 10^{-12}\hat{I}{»}^3$ magnetic resonator mode volume and to the low noise of the parametric amplifier, the spectrometer sensitivity reaches $260\pm 40$ spins$/$echo and $65\pm 10$ $\mathrm{spins}/\sqrt{\text{Hz}}$, respectively.

6 pages, 4 figures