Quantum Readout Error Mitigation and Precision Metric Based on Detector Tomography

Quantum technologies rely heavily on the accurate readout of quantum systems. Various noise sources create a need for quantum readout error mitigation, even post fault-tolerance. We use quantum detector tomography (QDT) to characterize the measurement process and use this information for more accurate quantum state tomography (QST). This method is largely readout mode-, architecture-, and noise source-independent. We present an infidelity convergence based benchmarking method for qubit readout which goes beyond the often used assignment fidelity. We test our readout error mitigation method on superconducting transmon qubits by studying how well it can mitigate common readout noise, such as insufficient amplification and suboptimal readout photon population. In the case of strong readout noise, we observe decreases in readout infidelity by a factor of up to 30. Due to the potential of 3-qubit entangling gates, we perform readout error mitigated quantum state tomography on a three qubit system and show significant improvements even with strong readout noise present. Our investigations reveal that neither quantum nor classical qubit readout correlation coefficients are induced even by high levels of readout noise, qualifying them as a further useful benchmark for optimal qubit readout.