Path-Independent Gates for Error-Corrected Quantum Computing: Experiment

In future fault-tolerant quantum computers, errors resulting from noise and decoherence must be detected and corrected in real-time. This is particularly important while applying logical gates, which can cause errors to quickly spread throughout the system.
Here, we present an error-corrected construction for a logical gate set [1] enacted by a multilevel transmon ancilla on a cavity-encoded logical qubit. We show that the logical information is maintained by detecting ancilla errors and applying the appropriate corrections to the logical qubit. The error-corrected operation is path-independent of dominant ancilla errors, leading to a sixfold suppression of the gate error with increased energy relaxation, and a fourfold suppression with increased dephasing noise. The results support the viability of hardware-efficient bosonic quantum computation by showing that bosonic qubits can be controlled by error-prone ancillas without inheriting their inferior performance.

[1] P. Reinhold et al., arXiv:1907.12327 (2019).