Wideband superconducting nanotube electrometer

TL;DR

This paper demonstrates a wideband superconducting nanotube electrometer operating at microwave frequencies, capable of detecting charge variations with high sensitivity without matching circuits, based on Josephson junctions.

Contribution

It introduces a novel superconducting nanotube electrometer that functions at high frequencies and provides a detailed analysis of its microwave response and charge detection capabilities.

Findings

Operates effectively at 600-900 MHz

Achieves charge sensitivity of 3.1×10⁻⁵ e/√Hz

Matches theoretical resistively and capacitively shunted junction model

Abstract

We have investigated the microwave response of nanotube Josephson junctions at 600-900 MHz at microwave powers corresponding to currents from 0 to $2\times I_{\mathrm C}$ in the junction. Compared with theoretical modeling, the response of the junctions correspond well to the lumped element model of resistively and capacitively shunted junction. We demonstrate the operation of these superconducting FETs as charge detectors at high frequencies without any matching circuits. Gate-voltage-induced charge $Q_{\rm G}$ modifies the critical current $I_{\rm C}$, which changes the effective impedance of the junction under microwave irradiation. This change, dependent on the transfer characteristics $dI_{\mathrm C}/dQ_{\rm G}$, modifies the reflected signal and it can be used for wide band electrometry. We measure a sensitivity of $3.1\times10^{-5}$ $e/\sqrt{\mathrm{Hz}}$ from a sample which has a maximum switching current of 2.6 nA.