Entangled quantum probes for dynamical environmental noise

TL;DR

This paper demonstrates that entangled quantum probes can significantly improve the estimation of environmental noise correlation times, especially in regimes where the noise is faster than a certain threshold, without requiring dynamical control.

Contribution

It introduces a measurement scheme using entangled probes to enhance noise characterization, identifying optimal conditions and robustness against decoherence.

Findings

Joint measurements on entangled probes outperform sequential single-qubit strategies.

Optimal probe states are multiqubit GHZ states when entanglement is beneficial.

The scheme remains effective despite probe depolarization or dephasing.

Abstract

We address the use of entangled qubits as quantum probes to characterize the noise induced by complex environments. In particular, we show that a joint measurement on entangled probes can improve estimation of the correlation time for a broad class of environmental noises compared to any sequential strategy involving single qubit preparation. The enhancement appears when the noise is faster than a threshold value, a regime which may always be achieved by tuning the coupling between the quantum probe and the environment inducing the noise. Our scheme exploits time-dependent sensitivity of quantum systems to decoherence and does not require dynamical control on the probes. We derive the optimal interaction time and the optimal probe preparation, showing that it corresponds to multiqubit GHZ states when entanglement is useful. We also show robustness of the scheme against depolarization or dephasing of the probe, and discuss simple measurements approaching optimal precision.