Nonequilibrium thermometry via an ensemble of initially correlated qubits

Abstract: We investigate an nonequilibrium quantum thermometry protocol in which an ensemble of qubits, acting as temperature probes, is weakly coupled to a macroscopic thermal bath. The temperature of the bath, the parameter of interest, is encoded in the dissipator of a Markovian thermalization process. For some relevant initial states, we observe a peak in the Quantum Fisher Information (QFI) during the transient of the thermalization, indicating enhanced sensitivity in early-time dynamics. This effect becomes more pronounced at higher bath temperatures and is further enhanced when the qubits' initial state has a larger ground-state population. Our analysis shows that both local coherence in the probes' initial state and initial correlations among the probes contribute to the amplification of the peak in the QFI, thus improving the precision of the temperature estimation. The influence of quantum correlations emerges as a central feature of this work. Although the dynamics does not permit superlinear scaling of the QFI with the number of probes, we identify the most effective initial states for designing high-precision quantum sensors within this setting. We also provide concrete guidelines for experimental implementations.