Assessing the Influence of Broadband Instrumentation Noise on Parametrically Modulated Superconducting Qubits

TL;DR

This paper investigates how broadband instrumentation noise affects flux stability and error rates in parametrically modulated superconducting qubits, proposing filtering techniques to improve gate fidelity.

Contribution

It introduces a model linking instrumentation noise to qubit dephasing and demonstrates noise reduction via filtering at the AC sweet spot.

Findings

Broadband noise increases flux instability and error rates.

Low-pass filtering reduces qubit sensitivity to flux noise.

The proposed framework guides noise floor requirements for high-fidelity gates.

Abstract

With superconducting transmon qubits --- a promising platform for quantum information processing --- two-qubit gates can be performed using AC signals to modulate a tunable transmon's frequency via magnetic flux through its SQUID loop. However, frequency tunablity introduces an additional dephasing mechanism from magnetic fluctuations. In this work, we experimentally study the contribution of instrumentation noise to flux instability and the resulting error rate of parametrically activated two-qubit gates. Specifically, we measure the qubit coherence time under flux modulation while injecting broadband noise through the flux control channel. We model the noise's effect using a dephasing rate model that matches well to the measured rates, and use it to prescribe a noise floor required to achieve a desired two-qubit gate infidelity. Finally, we demonstrate that low-pass filtering the AC signal used to drive two-qubit gates between the first and second harmonic frequencies can reduce qubit sensitivity to flux noise at the AC sweet spot (ACSS), confirming an earlier theoretical prediction. The framework we present to determine instrumentation noise floors required for high entangling two-qubit gate fidelity should be extensible to other quantum information processing systems.