Erasure Qubits: Overcoming the T1 Limit in Superconducting Circuits

The amplitude-damping time T1 has long stood as the major factor limiting quantum fidelity in superconducting circuits, prompting concerted efforts in the material science and design of qubits aimed at increasing T1. In contrast, the dephasing time Tϕ can usually be extended above T1 (via, e.g., dynamical decoupling) to the point where it does not limit fidelity. In this article, we propose a scheme for overcoming the conventional T1 limit on fidelity by designing qubits in a way that amplitude-damping errors can be detected and converted into erasure errors. Compared to standard qubit implementations, our scheme improves the performance of fault-tolerant protocols, as numerically demonstrated by the circuit-noise simulations of the surface code. We describe two simple qubit implementations with superconducting circuits and discuss procedures for detecting amplitude-damping errors, performing entangling gates, and extending Tϕ. Our results suggest that engineering efforts should focus on improving Tϕ and the quality of quantum coherent control, as they effectively become the limiting factor on the performance of fault-tolerant protocols.2 MoreReceived 15 August 2022Revised 2 July 2023Accepted 30 August 2023DOI:https://doi.org/10.1103/PhysRevX.13.041022Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum error correctionQuantum gatesQuantum information architectures & platformsQuantum Information, Science & Technology