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<p>We revisit the problem of the thermalization process for an Unruh-DeWitt (UDW) detector in de Sitter space. We derive the complete dynamics of the detector in the context of an open quantum system, without utilizing Markovian or RWA approximations. We employ quantum Fisher information (QFI) to estimate the Hubble parameter, which serves as a process function to distinguish the thermalization paths in the detector’s Hilbert space, determined by its local properties, including the detector’s energy gap and its initial state preparation, or by the global spacetime geometry. We find that the non-Markovian contribution generally reduces the QFI compared to the Markovian approximated solution. Regarding arbitrary initial states, the late-time QFI converges to an asymptotic value. In particular, we are interested in the background field within the one-parameter family of α-vacua in de Sitter space. We show that for general choices of <i>α</i>-vacuum, the asymptotic values of the converged QFI are significantly suppressed compared to previously known results for the Bunch-Davies vacuum.</p>

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Quantum Fisher information of a cosmic qubit undergoing non-Markovian de Sitter evolution

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  • 发表日期：

    2025年6月4日

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  • Langxuan Chen,
  • Jun Feng

摘要

We revisit the problem of the thermalization process for an Unruh-DeWitt (UDW) detector in de Sitter space. We derive the complete dynamics of the detector in the context of an open quantum system, without utilizing Markovian or RWA approximations. We employ quantum Fisher information (QFI) to estimate the Hubble parameter, which serves as a process function to distinguish the thermalization paths in the detector’s Hilbert space, determined by its local properties, including the detector’s energy gap and its initial state preparation, or by the global spacetime geometry. We find that the non-Markovian contribution generally reduces the QFI compared to the Markovian approximated solution. Regarding arbitrary initial states, the late-time QFI converges to an asymptotic value. In particular, we are interested in the background field within the one-parameter family of α-vacua in de Sitter space. We show that for general choices of α-vacuum, the asymptotic values of the converged QFI are significantly suppressed compared to previously known results for the Bunch-Davies vacuum.