Dual-state purification for practical quantum error mitigation

Quantum error mitigation is essential for many computing tasks on the noisy quantum computer with a limited number of qubits. In this paper, we propose practical protocol by virtually purifying state without qubit overhead or requiring only one ancilla qubit. dual-state purification, effectively generate purified increased fidelity using erroneous and its dual state, respectively, prepared circuit map inverse circuit. Combined tomography can make sure that final estimate an observable obtained from pure state. While absolute increases, numerical result, based depolarizing model, suggests our reduces compared to case rescaling factor decreasing depth; i.e., relative performance purification better larger circuits. On cloud computer, successfully demonstrate reduced variational eigensolver