Model-free readout-error mitigation for quantum expectation values

Measurements on current quantum processors are subject to hardware imperfections that lead readout errors. These errors manifest themselves as a bias in expectation values. Here, we propose very simple method forces the value appear multiplicative factor can be measured directly and removed at cost of an increase sampling complexity for observable. The assumes no specific form noise, but only requires noise is `weak' avoid excessive overhead. We provide bounds relating error sample complexity.