Inverted-circuit zero-noise extrapolation for quantum gate error mitigation

Current quantum computing hardware suffers from errors due to environmental effects, nearest neighbour interactions and imperfect gate operations. Techniques such as zero-noise extrapolation (ZNE) mitigate errors rather than eliminate them, and can be used with current hardware. For the ZNE, it is essential to know the exact noise gain factor so that an effective extrapolation can be performed. We propose a method for estimating the error strength occurring in a given quantum circuit in order to improve the results of zero-noise extrapolation. The circuit error rate is increased by inserting a sequence of gates that are equivalent to the identity in the noise-free case. Furthermore, the impact of gate errors on expectation values of observables can be reduced by twirling, which converts arbitrary errors into stochastic Pauli errors. The use of adaptive spacing and a maximum for the noise scaling factors appears to be advantageous for zero-noise extrapolation. We present results of the inverted-circuit error mitigation technique and compare them to results of the conventional zero-noise extrapolation.