Single-qubit thermometry

TL;DR

This paper explores how a single qubit can be used to distinguish between two temperatures of a bosonic bath, showing that initial coherence and entanglement can improve thermometric accuracy.

Contribution

It introduces a novel approach to quantum thermometry using a single qubit, highlighting the benefits of initial coherence and entanglement over simple equilibration methods.

Findings

Optimal measurement depends on interaction time.

Initial quantum coherence enhances temperature discrimination.

Entanglement with an ancillary qubit improves accuracy.

Abstract

Distinguishing hot from cold is the most primitive form of thermometry. Here we consider how well this task can be performed using a single qubit to distinguish between two different temperatures of a bosonic bath. In this simple setting, we find that letting the qubit equilibrate with the bath is not optimal, and depending on the interaction time it may be advantageous for the qubit to start in a state with some quantum coherence. We also briefly consider the case that the qubit is initially entangled with a second qubit that is not put into contact with the bath, and show that entanglement allows for even better thermometry.