Decoherence of quantum wave packets due to interaction with conformal space-time fluctuations

One of the biggest problems faced by those attempting to combine quantum theory and general relativity is the experimental inaccessibility of the unification scale. In this paper, we show how incoherent conformal waves in the gravitational field, which may be produced by quantum mechanical zero-point fluctuations, interact with the wave packets of massive particles. The result of this interaction is to produce decoherence within the wave packets which could be accessible in experiments at the atomic scale. Using a simple nonlinear model for the coherence properties of the gravitational field, we derive an equation for the evolution of the density matrix of such a wave packet. Following the primary state diffusion programme, the most promising source of space-time fluctuations for experimental detection is these zero-point energy fluctuations. According to our model, the absence of intrinsic irremovable decoherence in matter interferometry experiments puts bounds on some of the parameters of quantum gravity theories. Current experiments give lambda > 18, where lambda t(Planck) is an effective cut-off for the validity of low-energy quantum gravity theories.