Killing Horizons Decohere Quantum Superpositions

Understand

We recently showed that if a massive (or charged) body is put in a quantum spatial superposition, the mere presence of a black hole in its vicinity will eventually decohere the superposition.

• In this paper we show that, more generally, decoherence of stationary superpositions will occur in any spacetime with a Killing horizon.
• This occurs because, in effect, the long-range field of the body is registered on the Killing horizon which, we show, necessitates a flux of "soft horizon gravitons/photons" through the horizon.
• The Killing horizon thereby harvests "which path" information of quantum superpositions and will decohere any quantum superposition in a finite time.