Investigating the variance increase of readout error mitigation through\n classical bit-flip correction on IBM and Rigetti quantum computers

Readout errors are among the most dominant errors on current noisy\nintermediate-scale quantum devices. Recently, an efficient and scaleable method\nfor mitigating such errors has been developed, based on classical bit-flip\ncorrection. In this talk, we compare the performance of this method for IBM's\nand Rigetti's quantum devices, demonstrating how the method improves the noisy\nmeasurements of observables obtained on the quantum hardware. Moreover, we\nexamine the variance amplification to the data after applying of our mitigation\nprocedure, which is common to all mitigation strategies. We derive a new\nexpression for the variance of the mitigated Pauli operators in terms of the\ncorrected expectation values and the noisy variances.Our hardware results show\ngood agreement with the theoretical prediction, and we demonstrate that the\nincrease of the variance due to the mitigation procedure is only moderate.\n