Quantum thermometry for ultralow temperatures using probe and ancilla qubit chains

Abstract: We propose a scheme to enhance the range and precision of ultralow temperature measurements by employing a probe qubit coupled to a chain of ancilla qubits. Specifically, we analyze a qubit chain governed by Heisenberg $XX$ and Dzyaloshinskii-Moriya (DM) interactions. The precision limits of temperature measurements are characterized through the evaluation of quantum Fisher information (QFI). Our findings demonstrate that the achievable precision bounds, as well as the number of peaks in the QFI as a function of temperature, can be controlled by adjusting the number of ancilla qubits and the system's model parameters. These results are interpreted in terms of the influence of energy transitions on the range and the number of QFI peaks as a function of temperature. This study highlights the potential of the probe qubit-ancilla chain system as a powerful and precise tool for quantum thermometry in the ultralow temperature regime.