Methods for Measuring Magnetic Flux Crosstalk Between Tunable Transmons

TL;DR

This paper introduces three precise measurement techniques for quantifying magnetic flux crosstalk between tunable transmons, linking crosstalk levels to two-qubit gate fidelity in quantum computing.

Contribution

It develops new metrics for flux crosstalk, connects AC crosstalk to gate infidelity, and empirically studies crosstalk effects using quantum process tomography.

Findings

Crosstalk measurement sensitivities as fine as 0.001%

Quantitative link between AC flux crosstalk and gate infidelity

Empirical analysis of crosstalk impact on two-qubit gate fidelity

Abstract

In the gate model of quantum computing, a program is typically decomposed into a sequence of 1- and 2-qubit gates that are realized as control pulses acting on the system. A key requirement for a scalable control system is that the qubits are addressable - that control pulses act only on the targeted qubits. The presence of control crosstalk makes this addressability requirement difficult to meet. In order to provide metrics that can drive requirements for decreasing crosstalk, we present three measurements that directly quantify the DC and AC flux crosstalk present between tunable transmons, with sensitivities as fine as 0.001%. We develop the theory to connect AC flux crosstalk measures to the infidelity of a parametrically activated two-qubit gate. We employ quantum process tomography in the presence of crosstalk to provide an empirical study of the effects of crosstalk on two-qubit gate fidelity.