Four-qubit experiment extends logical coherence with fixed recovery cycles

Researchers at the Chinese Academy of Sciences demonstrated a four-qubit control method that extended logical coherence from approximately T1/4 nanoseconds to beyond T1 nanoseconds. The laboratory system compiles error recovery into repeating, open-loop waveforms, avoiding the syndrome measurements and real-time feedback normally used to diagnose and correct errors. Frequency-selective drives apply local recovery rules inside a ring of superconducting transmon qubits, slowing logical decay under random Pauli-X disturbances. Spectral crowding can cause leakage, however, and the four-qubit result does not establish that the method will scale to the hundreds or thousands of stable qubits needed for fault-tolerant computation.