Improving Cutoff Frequency Estimation Accuracy with Initial Probe-environment Correlations

We investigate the effect of the initial probe-environment correlations in estimating the cutoff frequency which is one of the crucial parameters characterizing the environment of a quantum system. The two-qubit probe, referred to as a probe constructed by two qubits, is prepared in the product state and allowed to interact with the environment. Under the initial probe-environment correlations, we derive the analytic quantum Fisher information (QFI) and the corresponding quantum signal-to-noise ratio (QSNR), which quantify the estimation accuracy of the cutoff frequency. By comparing the QFI and QSNR with the initial probe-environment correlations to those without correlations, it shows that the initial probe-environment correlations can be used to improve the accuracy of estimating the cutoff frequency in the estimation scheme of two-qubit probes.