Joint Quantum Foundations and WINQ seminar
A superposed geometry refers to a quantum state in which spacetime itself exists in a superposition of different classical configurations, such as distinct metrics or topologies. Rather than treating geometry as a fixed classical background, this approach aligns with the expectation from quantum gravity that spacetime should exhibit quantum features—just like matter.
Recent research has explored superposed geometries in contexts ranging from quantum reference frames and relativistic quantum information to quantum field theory in curved spacetime. These studies have revealed novel effects such as indefinite causal structure, interference in detector responses, and modifications to entanglement and locality, offering operational insights into the quantum nature of spacetime and providing promising frameworks to test gravitational effects in table-top quantum experiments. In this talk I shall discuss about our recent investigation [https://arxiv.org/abs/2412.15870] on the phenomenon of entanglement harvesting, using two Unruh-DeWitt detectors interacting with a quantum scalar field where the spacetime background is modeled as a superposition of two quotient Minkowski spaces which are not related by diffeomorphisms. Our results demonstrate that the superposed nature of spacetime induces interference effects that can significantly enhance entanglement for both twisted and untwisted field. We compute the concurrence, which quantifies the harvested entanglement, as function of the energy gap of detectors and their separation. We find that it reaches its maximum when we condition the final spacetime superposition state to match the initial spacetime state. Notably, for the twisted field, the parameter region without entanglement exhibits a significant deviation from that observed in classical Minkowski space or even a single quotient Minkowski space.
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