G. B. P. Huber | Searcharxiv

arXiv2026

Robust multi-mode superconducting circuit optimized for quantum information processing

Multi-mode superconducting circuits offer a promising platform for engineering robust systems for quantum computation. Previous studies indicate that single-mode devices cannot be engineered to simultaneously exhibit resilience against multiple decoherence sources due to conflicting requirements. In contrast, multi-mode systems offer increased flexibility and have proven capable of overcoming these fundamental limitations. Here, we present a multi-mode device optimized for quantum information processing. It features an anharmonicity of a third of the qubit frequency and reduced energy dispersion caused by charge and magnetic flux fluctuations. It exhibits improvements over the fundamental errors limiting Transmon and Fluxonium coherence and control, achieving ratios between the total coherence time and the gate time $T_2/t_g$ one order of magnitude larger than Transmon and two times larger than Fluxonium for microwave charge drives, assuming equal dielectric and inductive loss quality factors and limited drive strength. It furthermore demonstrates robustness against fabrication errors, a major limitation in many proposed multi-mode devices.

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arXiv2025

Parametric multi-element coupling architecture for coherent and dissipative control of superconducting qubits

As systems for quantum computing keep growing in size and number of qubits, challenges in scaling the control capabilities are becoming increasingly relevant. Efficient schemes to simultaneously mediate coherent interactions between multiple quantum systems and to reduce decoherence errors can minimize the control overhead in next-generation quantum processors. Here, we present a superconducting qubit architecture based on tunable parametric interactions to perform two-qubit gates, reset, leakage recovery and to read out the qubits. In this architecture, parametrically driven multi-element couplers selectively couple qubits to resonators and neighbouring qubits, according to the frequency of the drive. We consider a system with two qubits and one readout resonator interacting via a single coupling circuit and experimentally demonstrate a controlled-Z gate with a fidelity of $98.30\pm 0.23 \%$, a reset operation that unconditionally prepares the qubit ground state with a fidelity of $99.80\pm 0.02 \%$ and a leakage recovery operation with a $98.5\pm 0.3 \%$ success probability. Furthermore, we implement a parametric readout with a single-shot assignment fidelity of $88.0\pm 0.4 \%$. These operations are all realized using a single tunable coupler, demonstrating the experimental feasibility of the proposed architecture and its potential for reducing the system complexity in scalable quantum processors.

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