Electron Spin Resonance at the Level of 10000 Spins Using Low Impedance Superconducting Resonators

TL;DR

This paper demonstrates highly sensitive electron spin resonance detection of approximately 20,000 spins using low impedance superconducting resonators combined with quantum-limited amplification, enabling single-shot measurements with high signal-to-noise ratio.

Contribution

The work introduces a novel ESR measurement technique with significantly increased coupling strength and sensitivity, surpassing traditional resonator designs.

Findings

Detected around 20,000 spins with SNR of 1 in a single shot

Achieved a coupling strength of 150 Hz, much higher than typical designs

Observed spin relaxation dominated by radiative decay into the resonator

Abstract

We report on electron spin resonance (ESR) measurements of phosphorus donors localized in a 200 square micron area below the inductive wire of a lumped element superconducting resonator. By combining quantum limited parametric amplification with a low impedance microwave resonator design we are able to detect around 20000 spins with a signal-to-noise ratio (SNR) of 1 in a single shot. The 150 Hz coupling strength between the resonator field and individual spins is significantly larger than the 1 - 10 Hz coupling rates obtained with typical coplanar waveguide resonator designs. Due to the larger coupling rate, we find that spin relaxation is dominated by radiative decay into the resonator and dependent upon the spin-resonator detuning, as predicted by Purcell.