Suppressing chaos with mixed superconducting qubit devices

TL;DR

This paper investigates how mixed superconducting qubit devices can suppress chaotic behavior by analyzing energy level statistics, revealing that combining different qubit types enhances localization and device performance.

Contribution

The study demonstrates that mixed anharmonicity qubit arrays improve localization resilience and provides a detailed analysis of level statistics across different qubit configurations.

Findings

Mixed qubit arrays show increased localization with higher coupling.

Alternating anharmonicity arrays are more resilient to disorder.

Results confirmed using generalized Bose-Hubbard models.

Abstract

In quantum information processing, a tension between two different tasks occurs: while qubits' states can be preserved by isolating them, quantum gates can be realized only through qubit-qubit interactions. In arrays of qubits, weak coupling leads to states being spatially localized and strong coupling to delocalized states. Here, we study the average energy level spacing and the relative entropy of the distribution of the level spacings (Kullback-Leibler divergence from Poisson and Gaussian Orthogonal Ensemble) to analyze the crossover between localized and delocalized (chaotic) regimes in linear arrays of superconducting qubits. We consider both transmons as well as capacitively shunted flux qubits, which enables us to tune the qubit anharmonicity. Arrays with uniform anharmonicity, comprising only transmons or flux qubits, display remarkably similar dependencies of level statistics on the coupling strength. In systems with alternating anharmonicity, for typical disorder in the qubit frequencies the localized regime is found to be more resilient to the increase in qubit-qubit coupling strength in comparison to arrays with a single qubit type. Our results, which we also confirm using generalized Bose-Hubbard models, support designing devices that incorporate different qubit types to achieve higher performances.