Mitigation of Crosstalk Errors in Quantum Measurements

In the present-day quantum information technologies, measurements are performed not only at the end of quantum state evolution but also between quantum circuits to connect short-depth quantum circuits, for instance, variational quantum algorithms. Furthermore, measurements also contain crosstalk errors, which cannot be factorized into individual readout errors. In this work, we investigate methods for mitigating measurement errors across multiple qubits, particularly measurement crosstalk that cannot be corrected by methods for correcting individual readout errors. We present mitigation protocols that generally suppress these errors by up to a percentage level across multiple qubits. We first demonstrate that mitigating measurement errors of individual qubits cannot eliminate measurement crosstalk errors. We then present methods for mitigating measurement readout errors across multiple qubits, accounting for crosstalk noise. Both methods rely on quantum detector tomography. We also present proof-of-principle demonstrations of measurement error mitigation on IBM quantum hardware.