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arXiv · 2509.17903

Noise Protected Logical Qubit in a Open Chain of Superconducting Qubits with Ultrastrong Interactions

Roberto Stassi·Shilan Abo·Daniele Lamberto·Ye-Hong Chen·Adam Miranowicz·Salvatore Savasta·Franco Nori
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Abstract

To achieve a fault-tolerant quantum computer, it is crucial to increase the coherence time of quantum bits. In this work, we theoretically investigate a system consisting of a series of superconducting qubits that alternate between XX and YY ultrastrong interactions. By considering the two-lowest energy eigenstates of this system as a {\it logical} qubit, we demonstrate that its coherence is significantly enhanced: both its pure dephasing and relaxation times are extended beyond those of individual {\it physical} qubits. Specifically, we show that by increasing either the interaction strength or the number of physical qubits in the chain, the logical qubit's pure dephasing rate is suppressed to zero, and its relaxation rate is reduced to half the relaxation rate of a single physical qubit. Single qubit and two-qubit gates can be performed with a high fidelity.

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Roberto Stassi, Shilan Abo, Daniele Lamberto, Ye-Hong Chen, Adam Miranowicz, Salvatore Savasta, Franco Nori. 2025-09-22. Noise Protected Logical Qubit in a Open Chain of Superconducting Qubits with Ultrastrong Interactions. https://arxiv.org/abs/2509.17903

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