Correlations in Noisy Measurements

Although a measurement on the computational basis is devised in quantum computing, e.g., cloud-based quantum computing services, a quantum measurement in a realistic scenario is noisy. In particular, a measurement readout error in the era of noisy-intermediate-scale-quantum technologies is significant. In this work, we consider measurements on multiple qubits in a realistic scenario and present a method of analyzing noise in the measurement. Correlations existing in a noisy measurement are of particular interest so that local and crosstalk errors are introduced: the existence of correlations in a measurement in cloud-based quantum computing services is verified. We then present quantification of local and crosstalk errors and apply it to a noisy measurement in a cloud-based quantum computing service. Our results that analyze measurement errors can be used to mitigate these errors.