Dressed-state relaxation in coupled qubits as a source of two-qubit gate errors

TL;DR

This paper reveals a frequency-dependent relaxation mechanism in coupled qubits caused by dressed-state energy splitting, which leads to specific two-qubit gate errors and impacts quantum coherence in various encoding schemes.

Contribution

It identifies and experimentally verifies a new relaxation channel at the dressed-state splitting frequency, extending understanding of decoherence in interacting qubits.

Findings

Gate errors scale with noise spectral density at 2g frequency

Dressed-state relaxation extends $T_{1 ho}$ concepts to coupled systems

Universal relaxation mechanism affects multiple qubit platforms

Abstract

Understanding error mechanisms in two-qubit gate operations is essential for building high-fidelity quantum processors. While prior studies predominantly treat dephasing noise as either Markovian or predominantly low-frequency, realistic qubit environments exhibit structured, frequency-dependent spectra. Here we demonstrate that noise at frequencies matching the dressed-state energy splitting--set by the inter-qubit coupling strength g--induces a distinct relaxation channel that degrades gate performance. Through combined theoretical analysis and experimental verification on superconducting qubits with engineered noise spectra, we show that two-qubit gate errors scale predictably with the noise power spectral density at frequency 2g, extending the concept of $T_{1\rho}$ relaxation to interacting systems. This frequency-selective relaxation mechanism, universal across platforms, enriches our understanding of decoherence pathways during gate operations. The same mechanism sets coherence limits for dual-rail or singlet-triplet encodings.