Radio-frequency characterization of a supercurrent transistor made of a carbon nanotube

M Mergenthaler,A Baumgartner,P J Leek,A Nersisyan,G A D Briggs,F J Schupp,N Ares,E A Laird,C Schönenberger

doi:10.1088/2633-4356/ac1d57

Abstract

A supercurrent transistor is a superconductor–semiconductor hybrid device in which the Josephson supercurrent is switched on and off using a gate voltage. While such devices have been studied using DC transport, radio-frequency measurements allow for more sensitive and faster experiments. Here a supercurrent transistor made from a carbon nanotube is measured simultaneously via DC conductance and radio-frequency reflectometry. The radio-frequency measurement resolves all the main features of the conductance data across a wide range of bias and gate voltage, and many of these features are seen more clearly. These results are promising for measuring other kinds of hybrid superconducting devices, in particular for detecting the reactive component of the impedance, which a DC measurement can never detect.

Highlights

When a Josephson junction is fabricated from a semiconductor, its superconducting properties depend on the semiconductor’s density of states
The noise is much lower, as expected for a high-frequency measurement. These results show that a supercurrent transistor can be measured at RF without affecting its operation, and make RF techniques promising for rapidly characterising such devices under a range of conditions
By comparing simultaneous RF and DC transport measurements of a carbon nanotube supercurrent transistor, this experiment shows that RF reflectometry is sensitive to all the main transport features, most of which appear more distinctly than in DC transport alone

Summary

INTRODUCTION

When a Josephson junction is fabricated from a semiconductor, its superconducting properties depend on the semiconductor’s density of states. Supercurrent transistors are components of low-temperature electronics such as SQUID magnetometers [2] and gatemon qubits [3, 4] They can be used to measure level crossings [5] and chiral states [6] in junctions containing quantum dots, and to investigate correlated-electron behaviour such as charge localisation [7]. We use simultaneous RF reflectometry and DC measurements to characterise a supercurrent transistor made of a carbon nanotube We compare these two methods across the full operating regime of the device in bias and gate voltage. The noise is much lower, as expected for a high-frequency measurement These results show that a supercurrent transistor can be measured at RF without affecting its operation, and make RF techniques promising for rapidly characterising such devices under a range of conditions

DEVICE AND MEASUREMENT SETUP

DC SPECTROSCOPY

SPECTROSCOPY USING RF REFLECTOMETRY

Findings

CONCLUSION