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

TL;DR

This paper demonstrates a highly sensitive electron spin resonance spectroscopy technique at millikelvin temperatures, achieving detection of as few as 65 spins per root Hz using a superconducting micro-resonator and Josephson parametric amplifier.

Contribution

The work introduces a novel ESR spectrometer with unprecedented sensitivity, combining a superconducting micro-resonator and parametric amplifier for single-digit spin detection.

Findings

Achieved 260±40 spins per echo sensitivity.

Reached 65±10 spins/√Hz sensitivity.

Operated at millikelvin temperatures with a 7 GHz resonator.

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 ${\sim}10^{-12}\lambda^3$ magnetic resonator mode volume and to the low noise of the parametric amplifier, the spectrometer sensitivity reaches $260\pm40$ spins$/$echo and $65\pm10$ $\mathrm{spins}/\sqrt{\text{Hz}}$, respectively.