Improving the estimation of the environment parameters via a two-qubit scheme

TL;DR

This paper shows that using two qubits coupled to a common environment significantly enhances the accuracy of estimating environmental parameters compared to single-qubit methods, especially for super-Ohmic environments.

Contribution

The study introduces a two-qubit scheme that leverages indirect qubit interactions to vastly improve environment parameter estimation over traditional single-qubit approaches.

Findings

Two-qubit scheme greatly improves estimation precision.

Order-of-magnitude enhancement for super-Ohmic environments.

Quantum Fisher information quantifies the improvement.

Abstract

We demonstrate how using two qubits can drastically improve the estimation of environment parameters as compared to using only a single qubit. The two qubits are coupled to a common harmonic oscillatorenvironment, and the properties of the environment are imprinted upon the dynamics of the two qubits. The reduced density matrix of only one of these qubits contains a decoherence factor as well as an additional factor taking into account the indirect interaction induced between the qubits due to the interaction with their common environment. This additional factor can drastically improve the estimation of the environment parameters, as quantified by the quantum Fisher information. In particular, we investigate the estimation of the cutoff frequency, the coupling strength, and the temperature using our two-qubit scheme as compared to simply using a single qubit. For super-Ohmic environments in particular, one can improve the precision of the estimates by orders of magnitude.