Study of processes at the interface of quantum theory and gravity is an important research program that has the potential to yield useful insights for quantum gravity. One of the starting points for this program is to extend the framework of quantum field theory to curved spacetime, which is the so called framework of semi-classical gravity. A number of well known physical processes, such as Hawking and Unruh effects, were postulated by employing this approach and will be followed throughout by the material presented in this talk. From the gravity side, the principle of equivalence plays an important role in understanding physical effects in curved spacetime. It is often exploited to generalize classical as well as quantum processes in flat to curved spacetime. In this talk, I will present some interesting and non-trivial effects that were revealed from our studies, which are not usually evident when one uses the principle of equivalence. I will start by describing our analysis on what effects can be evoked in a local frame of reference if we can incorporate, in a specific way, the cosmological constant into a local patch of spacetime. Then, I will shift my focus toward the effect of curvature on quantum probes coupled to the quantum field. The use of two-level particle detector models, such as the Unruh-de Witt detector (UdW), that act as a quantum probe which responds to fluctuations in the quantum field will be highlighted. I will elucidate some results where we found that in the presence of gravity, an accelerated or rotating detector can couple with the tidal acceleration due to curvature and affect the response of a detector. Further, I will also emphasize 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. We propose that the features induced in entanglement can facilitate the use of entanglement as a probe of spacetime curvature.

Refs:
[1] Hari K and Dawood Kothawala, Phys. Rev. D 101, 124066 (2020).
[2] Hari K and Dawood Kothawala, Phys. Rev. D 104, 064032 (2021).
[3] Hari K and Dawood Kothawala, arXiv:2307.16413 [gr-qc].
[4] Hari K, Subhajit Barman and Dawood Kothawala, arXiv:2311.15019 [gr-qc].