# Collisional quantum thermometry

## TL;DR

This paper presents a new framework for quantum thermometry using collisional models, demonstrating that collective measurements can surpass traditional bounds and improve temperature estimation accuracy.

## Contribution

It introduces a general collisional model framework for quantum thermometry, showing how correlated ancillas and collective measurements enhance precision beyond standard limits.

## Key findings

- Ancillas can outperform the thermal Cramer-Rao bound.
- Collective measurements lead to superlinear Fisher information scaling.
- The approach is effective even with weak system-ancilla interactions.

## Abstract

We introduce a general framework for thermometry based on collisional models, where ancillas probe the temperature of the environment through an intermediary system. This allows for the generation of correlated ancillas even if they are initially independent. Using tools from parameter estimation theory, we show through a minimal qubit model that individual ancillas can already outperform the thermal Cramer-Rao bound. In addition, due to the steady-state nature of our model, when measured collectively the ancillas always exhibit superlinear scalings of the Fisher information. This means that even collective measurements on pairs of ancillas will already lead to an advantage. As we find in our qubit model, such a feature may be particularly valuable for weak system-ancilla interactions. Our approach sets forth the notion of metrology in a sequential interactions setting, and may inspire further advances in quantum thermometry.