Temperature Estimation of Quantum Environments using Impurity Probes

Recent studies have made great advances in designing temperature probing schemes using quantum parameter estimation strategies. While the problem of accurate temperature

estimation is of foundational importance, it is also crucially relevant in the NISQ era and for many experimental setups. Here we study quantum impurity models as a platform for

quantum thermometry. In particular, we critically assess the thermometric capabilities of an Ising and Kondo impurity probe in different fermionic thermal environments. We find that

the Ising impurity has sensing capabilities independent of the environment being probed, with maximum sensitivity at tunable temperatures, controlled by applied magnetic fields.

However, as with the idealized free qubit probe, the Ising impurity has no thermalization mechanism. By contrast, the more realistic Kondo impurity can thermalize but this same

mechanism necessarily results in entanglement with the environment, thereby lowering thermometric sensitivity. Interestingly, the low-temperature Kondo probe response takes a

characteristic universal form, albeit at the expense of poorer overall sensitivity. Sensitivity in the high temperature regime approaches that of the Ising probe. This suggests that realistic

quantum impurity probes can act as robust and versatile thermometers.