A calculation showing that a spatial quantum superposition held by an observer at the center of de Sitter spacetime is decohered by emitting soft scalar, electromagnetic, or gravitational radiation across the cosmological horizon. Using the algebraic approach to quantum field theory on curved spacetime, the number of entangling particles emitted is written directly in terms of the field's local two-point correlation function in the de Sitter-invariant vacuum, growing linearly with the time the superposition is held, which fixes the previously undetermined numerical prefactor of the gravitational decoherence rate.
This paper computes, from the viewpoint of a local observer, how a spatial quantum superposition held at the center of de Sitter spacetime is decohered by the cosmological horizon. Using the algebrai…