Qubits with predominantly erasure errors present distinctive advantages for quantum error correction(QEC) and fault tolerant quantum computing. Logical qubits based on dual-rail encoding that exploit erasure detection have been recently proposed in superconducting circuit architectures, either with coupled transmons or cavities. Here, we implement a dual-rail qubit encoded in a compact, double-post superconducting cavity. Using an auxiliary transmon, we perform erasure detection on the dual-rail subspace. We characterize the behaviour of the codespace by a novel method to perform joint-Wigner tomography. This is based on modifying the cross-Kerr interaction between the cavity modes and the transmon. We measure an erasure rate of 3.981 +/- 0.003 (ms)-1 and a residual dephasing error rate up to 0.17 (ms)-1 within the codespace. This strong hierarchy of error rates, together with the compact and hardware-efficient nature of this novel architecture, hold promise in realising QEC schemes with enhanced thresholds and improved scaling.
@article{arxiv.2311.04423,
title = {Erasure detection of a dual-rail qubit encoded in a double-post superconducting cavity},
author = {Akshay Koottandavida and Ioannis Tsioutsios and Aikaterini Kargioti and Cassady R. Smith and Vidul R. Joshi and Wei Dai and James D. Teoh and Jacob C. Curtis and Luigi Frunzio and Robert J. Schoelkopf and Michel H. Devoret},
journal= {arXiv preprint arXiv:2311.04423},
year = {2023}
}