Enhanced frequency and temperature estimation by a $\mathcal{PT}$-symmetric quantum oscillator

Abstract: Quantum metrology employs quantum properties to enhance the precision of physical parameters, in order to characterize quantum states as well as channels. Frequency and temperature estimations are of fundamental importance for these tasks and have been considerably treated in quantum sensing strategies. From the set of quantum features that can be exploited in quantum metrology, those related to non-Hermitian systems have received much attention in recent times. Here, we consider a paradigmatic non-Hermitian system, the quantum Swanson oscillator, as a probe system, in order to investigate how the non-Hermitian contribution affects the frequency and temperature estimation. We use the quantum Fisher information to compute the main results. Furthermore, to perform a fair comparison, we define a gain function which is the ratio between the quantum Fisher information with the non-Hermitian contribution and the quantum Fisher information when this term becomes Hermitian. In addition, the quantum Fisher information is discussed in terms of the energetic cost to include the non-Hermitian contribution. Given that we obtain the Hermitian counterpart of the Hamiltonian by applying the Dyson map, we also study the estimation of the parameters characterizing this mapping. Our results indicate that the non-Hermitian contribution in the Swanson quantum oscillator can contribute to enhance the frequency and temperature estimation.