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The two-level particle detector models, such as Unruh-de Witt detectors(UdW), that act as quantum probes to probe the dynamics of the quantum field, can play a significant role in understanding quantum effects in different frames of reference, such as the Unruh effect. These two-level quantum probes are used to study quantum field theory for different observers in flat spacetime as well as in curved spacetime. In the presence of gravity, an accelerated or rotating observer carrying such a quantum probe can couple with the tidal acceleration due to curvature and affect the response of a detector. For accelerated detectors, we found that the geodesic interval, which is an important quantity in determining the transition probability of the excitation of such detectors, can be partially resummed for general spacetime with certain assumptions. This allows us to determine the transition probability for the excitation of the detectors, which turns out to be a thermal spectrum. In the case of rotation, we studied the rotational motion in de Sitter and anti-de Sitter spacetimes and arrived at specific conditions for geodesic interval in anti-de Sitter spacetime for the detector to have a thermal spectrum. These findings are important since one might not discover these effects when the analysis is limited to leading order in curvature using the principle of equivalence. We also identified specific mappings for stationary motion in dS/AdS spacetime to stationary motion in Minkowski spacetime. Further, we will also explore the indirect yet universal role of spacetime curvature in creating entanglement between two quantum probes coupled to a scalar field in a suitable vacuum state. These quantum probes are not initially entangled and are placed at two causally disconnected points. The entanglement between the detectors is affected by the curvature of spacetime and can be elucidated by the deformation of the causal structure and deviation of detector trajectories due to the presence of curvature. We propose that the features induced in entanglement can facilitate the use of entanglement as a probe of spacetime.
Colloquium Committee