The quantum Fisher information in phase estimation is investigated for a qubit which is placed under the influence of a non-Markovian environment. The multi-mode Jaynes–Cummings model which has at least one excitation is used as a qubit-environment model. It is examined how initial correlation between the qubit and the environment affects time evolution of the quantum Fisher information. Although information on the phase parameter is included only in off-diagonal elements of the reduced density matrix of the qubit in the absence of the initial correlation, it is included not only in off-diagonal elements but also in diagonal elements in the presence of the initial correlation. This implies that the quantum Fisher information is greatly affected by the initial correlation. In particular, when the time evolution of the reduced density operator of the qubit is non-Markovian, the quantum Fisher information can take values greater than its initial value due to the initial correlation.
Quantum Information Processing – Springer Journals
Published: Aug 29, 2015
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