Gravity-mediated decoherence

A small quantum system within the gravitational field of a massive body will be entangled with the quantum degrees of freedom of the latter. Hence, the massive body acts as an environment, and it induces non-unitary dynamics, noise, and decoherence to the quantum system. It is impossible to shield systems on Earth from this gravity-mediated decoherence, which could severely affect all experiments with macroscopic quantum systems. We undertake a first-principles analysis of this effect, by deriving the corresponding open system dynamics. We find that near-future quantum experiments are not affected, but there is a strong decoherence effect at the human scale. The decoherence time for a superposition of two localized states of a human with an one meter separation is of the order of one second.