Sensitivity and Linearity of Superconducting Radio-Frequency Single-Electron Transistors: Effects of Quantum Charge Fluctuations

TL;DR

This study explores how quantum charge fluctuations influence the performance of superconducting RF-SETs, revealing that strong fluctuations can enhance linearity and noise performance while maintaining high charge sensitivity.

Contribution

It demonstrates that RF-SETs with strong quantum fluctuations remain operational and can outperform weak-fluctuation devices in linearity and noise characteristics.

Findings

RF-SETs operate effectively with quantum fluctuations for >1

Quantum fluctuations improve linearity and signal-to-noise ratio

Charge sensitivity remains excellent despite fluctuations

Abstract

We have investigated the effects of quantum fluctuations of quasiparticles on the operation of superconducting radio-frequency single-electron transistors (RF-SETs) for large values of the quasiparticle cotunneling parameter $\alpha=8E_{J}/E_{c}$, where $E_{J}$ and $E_{c}$ are the Josephson and charging energies. We find that for $\alpha>1$, subgap RF-SET operation is still feasible despite quantum fluctuations that renormalize the SET charging energy and wash out quasiparticle tunneling thresholds. Surprisingly, such RF-SETs show linearity and signal-to-noise ratio superior to those obtained when quantum fluctuations are weak, while still demonstrating excellent charge sensitivity.