Qubit error correction blocked by common measurement shortcut

A widely used technique for protecting quantum information is now understood to undermine the very error correction it intends to provide. Parity-measurement protocols, common in circuit quantum electrodynamics, corrupt logical information during continuous quantum error correction. The failure stems from approximating a three-body interaction with two-body couplings to the meter, preventing simultaneous suppression of measurement backaction. This work imposes a practical limitation on continuous stabilizer quantum error correction, suggesting a shift toward architectures realizing native three-body interactions or erasure-based encodings. Continuous quantum error correction relies on protocols that distinguish between logical and error subspaces, but approximations within these protocols introduce new errors. This corruption stems from a simplification in how the measurement apparatus, or “meter,” interacts with the qubits being measured. Instead of a true three-body interaction, where the meter interacts simultaneously with all qubits involved in the error correction, researchers have been approximating this with a sum of two-body couplings. This seemingly minor…