  Measurements on near-term quantum processors are inevitably subject to
hardware imperfections that lead to readout errors. Mitigation of such
unavoidable errors is crucial to better explore and extend the power of
near-term quantum hardware. In this work, we propose a method to mitigate
measurement errors in computing quantum expectation values using the truncated
Neumann series. The essential idea is to cancel the errors by combining various
noisy expectation values generated by sequential measurements determined by
terms in the truncated series. We numerically test this method and find that
the computation accuracy is substantially improved. Our method possesses
several advantages: it does not assume any noise structure, it does not require
the calibration procedure to learn the noise matrix a prior, and most
importantly, the incurred error mitigation overhead is independent of system
size, as long as the noise resistance of the measurement device is moderate.
All these advantages empower our method as a practical measurement error
mitigation method for near-term quantum devices.
