Quantum error mitigation for fault-tolerant quantum computing*

Fault-tolerant quantum computing (FTQC) implements universal quantum computing while suppressing physical errors via quantum error correction. Although the effective error rate decreases exponentially with the code distance, it is expected that the number of available physical qubits is restricted even after FTQC is realized in some form. Meanwhile, quantum error mitigation (QEM) was recently introduced for suppressing errors in Noisy Intermediate-Scale Quantum (NISQ) devices for improving computation accuracy of near-term quantum algorithms with its overhead being a greater number of samples. In this work, we show QEM can compensate dominant errors in FTQC without increasing the number of qubits. This scheme will dramatically alleviate required overheads of FTQC for achieving a high-accuracy quantum computing.