A Dual-rail Qubit with Parametrically Coupled Transmons

Quantum error correction (QEC) is essential for building fault-tolerant quantum computers. Although experiments across various platforms have demonstrated physical error rates below the surface code threshold, there remains a strong interest in developing more efficient QEC protocols to reduce resource overhead. One promising approach is the erasure qubit. The key idea of erasure qubits is to convert the dominant error in physical qubits into leakage outside the computational subspace, which can be efficiently detected and corrected with the right system architecture. To illustrate the potential of this approach, we introduce an erasure qubit where the logical qubit is encoded in the single-photon subspace of two parametrically coupled transmons, utilizing dual-rail encoding. In this talk, we will discuss how the design of our device, combined with dual-rail encoding, enhances the coherence of the erasure qubit. We achieve dual-rail single-qubit gates implemented with parametric interaction with high fidelity. Additionally, we show mid-circuit detection of erasure errors further improves performance by mitigating multiphoton errors.