Fig. 1 — Figure 1: Repetition code of bosonic qubits. (a) Schematic diagram of the repetition code device. Data qubits S1,⋯,S5,, (blue) are encodexternal image — opens at the sourceDrawings and plots. (a) Repetition-code schematic: five cat data qubits (cyan), each stabilised by a buffer mode (green), checked by four transmon ancillas (orange) that flag a phase-flip (Z) error; (b) chip layout drawing (1 mm scale bar) with storage resonators S1–S5; (c, d) close-ups of a buffer with its multi-pole filter and an ancilla with couplers and readout; (e) Bloch sphere of cat states; (f) bit-flip time rising exponentially and phase-flip time falling with mean photon number. From arXiv 2409.13025, Putterman et al., 'Hardware-efficient quantum error correction via concatenated bosonic qubits'. Superconducting cat qubits suppress bit flips in hardware, so the outer code only has to catch phase flips.