# Mitigation of readout noise in near-term quantum devices by classical post-processing based on detector tomography

## TL;DR

This paper introduces a classical post-processing method based on detector tomography to mitigate readout noise in near-term quantum devices, significantly improving measurement accuracy for various quantum tasks.

## Contribution

The authors develop a simple, practical scheme using detector tomography to correct readout errors caused by classical noise in quantum measurements on superconducting qubits.

## Key findings

- Significant error reduction in IBM and Rigetti quantum processors.
- Improved accuracy in quantum state and process tomography.
- Enhanced performance of quantum algorithms and probability distributions.

## Abstract

We propose a simple scheme to reduce readout errors in experiments on quantum systems with finite number of measurement outcomes. Our method relies on performing classical post-processing which is preceded by Quantum Detector Tomography, i.e., the reconstruction of a Positive-Operator Valued Measure (POVM) describing the given quantum measurement device. If the measurement device is affected only by an invertible classical noise, it is possible to correct the outcome statistics of future experiments performed on the same device. To support the practical applicability of this scheme for near-term quantum devices, we characterize measurements implemented in IBM's and Rigetti's quantum processors. We find that for these devices, based on superconducting transmon qubits, classical noise is indeed the dominant source of readout errors. Moreover, we analyze the influence of the presence of coherent errors and finite statistics on the performance of our error-mitigation procedure. Applying our scheme on the IBM's 5-qubit device, we observe a significant improvement of the results of a number of single- and two-qubit tasks including Quantum State Tomography (QST), Quantum Process Tomography (QPT), the implementation of non-projective measurements, and certain quantum algorithms (Grover's search and the Bernstein-Vazirani algorithm). Finally, we present results showing improvement for the implementation of certain probability distributions in the case of five qubits.