Superconducting Nanowires as Nonlinear Inductive Elements for Qubits

TL;DR

This paper investigates superconducting nanowires integrated into microwave resonators, demonstrating their nonlinear inductive behavior and potential for qubit applications through experimental measurements and a Duffing oscillator model.

Contribution

It introduces a novel approach to using superconducting nanowires as nonlinear inductive elements in microwave resonators and proposes their application in nanowire-based qubits.

Findings

Nonlinear resonance behavior dependent on supercurrent amplitude.

Observation of hysteretic bifurcation in high-Q resonators.

Validation of the Duffing oscillator model for nanowire-induced nonlinearity.

Abstract

We report microwave transmission measurements of superconducting Fabry-Perot resonators (SFPR), having a superconducting nanowire placed at a supercurrent antinode. As the plasma oscillation is excited, the supercurrent is forced to flow through the nanowire. The microwave transmission of the resonator-nanowire device shows a nonlinear resonance behavior, significantly dependent on the amplitude of the supercurrent oscillation. We show that such amplitude-dependent response is due to the nonlinearity of the current-phase relationship (CPR) of the nanowire. The results are explained within a nonlinear oscillator model of the Duffing oscillator, in which the nanowire acts as a purely inductive element, in the limit of low temperatures and low amplitudes. The low quality factor sample exhibits a "crater" at the resonance peak at higher driving power, which is due to dissipation. We observe a hysteretic bifurcation behavior of the transmission response to frequency sweep in a sample with a higher quality factor. The Duffing model is used to explain the Duffing bistability diagram. We also propose a concept of a nanowire-based qubit that relies on the current dependence of the kinetic inductance of a superconducting nanowire.