Error Mitigation

Error mitigation is a family of classical post-processing techniques that improve the accuracy of results from noisy quantum hardware without the full overhead of quantum error correction. Unlike QEC (which actively corrects errors in real time using many physical qubits), error mitigation uses statistical methods to extrapolate or filter out noise effects. Key techniques include: Zero Noise Extrapolation (ZNE) — run circuits at multiple noise levels and extrapolate to zero noise; Probabilistic Error Cancellation (PEC) — sample from a quasi-probability distribution to cancel noise; Measurement Error Mitigation — calibrate and correct readout errors; Clifford Data Regression — use classically-simulable circuits to learn noise properties. Error mitigation is crucial for NISQ-era VQE and QAOA experiments. It adds overhead (more shots, more classical computation) but significantly improves result quality. IBM Qiskit Runtime and HLQuantum both include built-in error mitigation.