Dissipative quantum Fisher information for a general Liouvillian parametrized process

摘要

The dissipative quantum Fisher information (DQFI) for a dynamic map with a general parameter in an open quantum system is investigated, which can be regarded as an analog of the quantum Fisher information in the Liouville space. We first derive a general dissipative generator in the Liouville space, and based on its decomposition form, find the DQFI stems from two parts. One is the dependence of eigenvalues of the Liouvillian supermatrix on the estimated parameter, which shows a linear dependence on time. The other is the variation of the eigenvectors with the estimated parameter. The relationship between this part and time presents rich characteristics, including harmonic oscillation, pure exponential gain and attenuation, as well as exponential gain and attenuation of oscillatory type, which depend specifically on the properties of the Liouville spectrum. This is in contrast to that of the conventional generator, where only oscillatory dependencies are seen. Particularly, we find that the nonunitary parameter encoding process induced by the dissipative generator can be transformed into two unitary encoding processes plus the contribution of the commutator between the two. Further, we illustrate the theory through a toy model: a two-level system with spin -flip noise. Especially, by using the DQFI, we demonstrated that the exceptional estimation precision cannot be obtained for this model at the Liouvillian exceptional point.

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