Measurement crosstalk between two phase qubits coupled by a coplanar waveguide

TL;DR

This paper investigates measurement crosstalk in coupled flux-biased phase qubits, showing that a coplanar waveguide cavity can significantly reduce crosstalk by acting as a bandpass filter, supported by experimental and classical modeling.

Contribution

It demonstrates experimentally and theoretically that a coplanar waveguide cavity reduces measurement crosstalk between phase qubits, introducing a simple classical model that aligns with observed data.

Findings

Crosstalk produces damped oscillations and frequency chirped noise.

The cavity acts as a bandpass filter reducing crosstalk.

Classical model agrees with experimental results.

Abstract

We analyze the measurement crosstalk between two flux-biased phase qubits coupled by a resonant coplanar waveguide cavity. After the first qubit is measured, the superconducting phase can undergo damped oscillations resulting in an a.c. voltage that produces a frequency chirped noise signal whose frequency crosses that of the cavity. We show experimentally that the coplanar waveguide cavity acts as a bandpass filter that can significantly reduce the crosstalk signal seen by the second qubit when its frequency is far from the cavity's resonant frequency. We present a simple classical description of the qubit behavior that agrees well with the experimental data. These results suggest that measurement crosstalk between superconducting phase qubits can be reduced by use of linear or possibly nonlinear resonant cavities as coupling elements.