Abstract

In the Unruh effect, long-distance correlations in a pure
quantum state cause accelerated observers to experience the state as a thermal
bath. We discuss a similar phenomenon for quantum states that contain
correlations between the distant future and the distant past. Examples include
Minkowski half-space with a static mirror and an eternal black hole with an
unusual global structure behind the horizon. The question of utilising the
future-past correlations in quantum information tasks is raised.