Realization of a quantum error detection code with a dynamically reassigned ancillary qubit

Quantum error correction (QEC) is essential for achieving fault-tolerant quantum computing. While superconducting qubits are among the most promising candidates for scalable QEC, their limited nearest-neighbor connectivity presents significant challenges for implementing a wide range of error correction codes. In this work, we experimentally demonstrate a quantum error detection scheme that employs a dynamically reassigned ancillary qubit on a chain of three linearly connected transmon qubits. We show that this scheme appears capable of achieving performance comparable to conventional static-ancilla circuits. Additionally, the approach facilitates efficient quantum state preparation, which we demonstrate with tomography of arbitrary logical states. Our results provide experimental evidence for a flexible strategy that could be used for implementing QEC codes under connectivity constraints and highlight a possible path toward scalable quantum architectures.