Quantum thermometry by single-qubit dephasing

TL;DR

This paper proposes a quantum thermometry method using a single qubit's dephasing dynamics to estimate environmental temperature without thermalization, optimizing precision via quantum Fisher information.

Contribution

It introduces a quantum scheme leveraging qubit dephasing sensitivity for temperature estimation, optimizing measurement parameters for maximum accuracy.

Findings

Optimal estimation depends on the interplay between dephasing dynamics and environment structure.

Maximum precision is achieved before the qubit reaches the stationary state.

Explicit measurement strategies attain the quantum Cramer-Rao bound.

Abstract

We address the dephasing dynamics of a qubit as an effective process to estimate the temperature of its environment. Our scheme is inherently quantum, since it exploits the sensitivity of the qubit to decoherence, and does not require thermalization with the system under investigation. We optimize the quantum Fisher information with respect to the interaction time and the temperature in the case of Ohmic-like environments. We also find explicitly the qubit measurement achieving the quantum Cramer- Rao bound to precision. Our results show that the conditions for optimal estimation originate from a non-trivial interplay between the dephasing dynamics and the Ohmic structure of the environment. In general, optimal estimation is achieved neither when the qubit approaches the stationary state, nor for full dephasing.