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arXiv · 2601.21616

A biased-erasure cavity qubit with hardware-efficient quantum error detection

Jiasheng Mai·Qiyu Liu·Xiaowei Deng·Yanyan Cai·Zhongchu Ni·Libo Zhang·Ling Hu·Pan Zheng·Song Liu·Yuan Xu·Dapeng Yu
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Abstract

Erasure qubits are beneficial for quantum error correction due to their relaxed threshold requirements. While dual-rail erasure qubits have been demonstrated with a strong error hierarchy in circuit quantum electrodynamics, biased-erasure qubits -- where erasures originate predominantly from one logical basis state -- offer further advantages. Here, we realize a hardware-efficient biased-erasure qubit encoded in the vacuum and two-photon Fock states of a single microwave cavity. The qubit exhibits an erasure bias ratio of over 265. By using a transmon ancilla for logical measurements and mid-circuit erasure detections, we achieve logical state assignment errors below 1% and convert over 99.3% leakage errors into detected erasures. After postselection against erasures, we achieve effective logical relaxation and dephasing rates of $(6.2~\mathrm{ms})^{-1}$ and $(3.1~\mathrm{ms})^{-1}$, respectively, which exceed the erasure error rate by factors of 31 and 15, establishing a strong error hierarchy within the logical subspace. These postselected error rates indicate a coherence gain of about 6.0 beyond the break-even point set by the best physical qubit encoded in the two lowest Fock states in the cavity. Moreover, randomized benchmarking with interleaved erasure detections reveals a residual logical gate error of 0.29%. This work establishes a compact and hardware-efficient platform for biased-erasure qubits, promising concatenations into outer-level stabilizer codes toward fault-tolerant quantum computation.

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Jiasheng Mai, Qiyu Liu, Xiaowei Deng, Yanyan Cai, Zhongchu Ni, Libo Zhang, Ling Hu, Pan Zheng, Song Liu, Yuan Xu, Dapeng Yu. 2026-01-29. A biased-erasure cavity qubit with hardware-efficient quantum error detection. https://arxiv.org/abs/2601.21616

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