What does measurement-error mitigation invert?

Question: In simple readout-error mitigation, what is commonly estimated and inverted or regularized? A) The complete Hamiltonian of the backend B) The matrix describing conditional probabilities of observed classical bitstrings given prepared computational-basis states C) The exact unitary matrix of the full quantum circuit D) The distribution of hidden variables before measurement Correct: B Explanation: Readout mitigation estimates a calibration matrix mapping true prepared basis states to observed classical outcomes. Correction attempts to invert this classical confusion process, often with regularization or constraints to avoid unstable results. Topic: advanced quantum computing / readout mitigation / measurement noise