Superconducting Parallel-Plate Resonators for the Detection of Single Electron Spins

TL;DR

This paper presents a novel superconducting microwave resonator design optimized for detecting single electron spins, achieving high coupling strength, a very high Purcell factor, and robust performance in magnetic fields.

Contribution

The paper introduces a multilayer superconducting resonator with ultra-high Purcell factor and demonstrates fabrication methods, high quality factors, and magnetic field resilience for single-spin detection.

Findings

Achieved Purcell factor > 10^15

Intrinsic Q-factor > 2 x 10^4 at single-photon level

Resonators operate effectively in magnetic fields up to 500 mT

Abstract

We introduce a multilayer superconducting microwave resonator with sub-Ohm impedance optimized for high coupling strength to single electron spins. The design minimizes the magnetic far-field and therefore achieves a Purcell factor $F_P > 10^{15}$. We show several ways to fabricate this type of resonator and present resonators with an intrinsic $Q$-factor exceeding $2 \cdot 10^4$ at the single-photon level. We further characterize these resonators in magnetic fields up to $500 \, \text{mT}$. Finally, we evaluate the impact of the achievable Purcell factor on single-spin detection through photon counting and dispersive readout.