Optimal multiparameter quantum estimation in accelerating Unruh-DeWitt detectors

TL;DR

This paper explores the fundamental limits of estimating Unruh temperature and initial state parameters in relativistic quantum systems, analyzing effects of environmental noise and non-Markovian dynamics on measurement precision.

Contribution

It introduces a comprehensive framework for multiparameter quantum estimation in relativistic settings, considering open system effects and environmental noise.

Findings

Parameters are quantum compatible in noiseless conditions.

Non-Markovian effects can temporarily enhance estimation precision.

Dissipative noise causes more significant precision loss than dephasing.

Abstract

The quantum Fisher information matrix (QFIM) is central to multiparameter quantum metrology, dictating the attainable sensitivity via the quantum Cram\'er-Rao bound. In this work, we investigate the ultimate precision limits for relativistic quantum thermometry in a bipartite system of uniformly accelerated Unruh-DeWitt detectors. Utilizing the symmetric logarithmic derivative (SLD) formalism within the QFIM framework, we analyze the individual and simultaneous estimation of the Unruh temperature $T$ and the initial-state parameter $\Delta_0$. In the noiseless case, we demonstrate that these two parameters are quantum compatible, allowing the multiparameter quantum Cram\'er-Rao bound to be saturated without a loss of precision. We then examine the impact of environmental effects by comparing Markovian and non-Markovian dynamics. In the Markovian regime, dissipation leads to a monotonic degradation of estimation precision; conversely, non-Markovian memory effects induce temporal oscillations and transient precision enhancements due to information backflow. The robustness of the estimation protocols is further analyzed under correlated noisy channels, including amplitude damping, phase flip, and phase damping. We show that dissipative noise results in more significant precision loss than purely dephasing mechanisms, whereas classical correlations in the noise mitigate this degradation. Finally, we discuss the estimation of the detector energy-level spacing $\omega$ as a natural extension, highlighting its sensitivity to the environmental structure. Our results provide a unified framework for relativistic multiparameter quantum metrology within the context of open quantum systems.