Encoding a magic state with beyond break-even fidelity

We distill magic states to complete a universal set of fault-tolerant logic gates that is needed for large-scale quantum computing. By encoding better quality input states for our distillation procedure, we can reduce the considerable resource cost of producing magic states. We demonstrate an error-suppressed encoding scheme for a two-qubit input magic state, that we call the CZ state, on an array of superconducting qubits. Using a complete set of projective logical Pauli measurements, that are also tolerant to a single circuit error, we propose a circuit that demonstrates a magic state prepared with infidelity $(1.87 \pm 0.16) \times 10^{-2}$. Additionally, the yield of our scheme increases with the use of adaptive circuit elements that are conditioned in real time on mid-circuit measurement outcomes. We find our results are consistent with variations of the experiment, including where we use only post-selection in place of adaptive circuits, and where we interrogate our output state using quantum state tomography on the data qubits of the code. Remarkably, the error-suppressed preparation experiment demonstrates a fidelity exceeding that of the preparation of the same unencoded magic-state on any single pair of physical qubits on the same device.