Bounds on collapse models from cold-atom experiments

TL;DR

This paper uses ultracold atomic experiments to set bounds on collapse models, showing that non-Markovian effects do not alter these bounds and analyzing the impact of dissipative effects at different noise temperatures.

Contribution

It provides new bounds on collapse models from cold-atom experiments and demonstrates their robustness against non-Markovian effects.

Findings

Bounds on collapse models are tighter than previous atomic experiments.

Non-Markovian effects do not significantly alter the bounds.

Dissipative effects are negligible at high temperatures but relevant at low temperatures.

Abstract

The spontaneous localization mechanism of collapse models induces a Brownian motion in all physical systems. This effect is very weak, but experimental progress in creating ultracold atomic systems can be used to detect it. In this paper, we considered a recent experiment [1], where an atomic ensemble was cooled down to picokelvins. Any Brownian motion induces an extra increase of the position variance of the gas. We study this effect by solving the dynamical equations for the Continuous Spontaneous Localizations (CSL) model, as well as for its non-Markovian and dissipative extensions. The resulting bounds, with a 95% of confidence level, are beaten only by measurements of spontaneous X-ray emission and by experiments with cantilever (in the latter case, only for rC > 10^(-7) m, where rC is one of the two collapse parameters of the CSL model). We show that, contrary to the bounds given by X-ray measurements, non-Markovian effects do not change the bounds, for any reasonable choice of a frequency cutoff in the spectrum of the collapse noise. Therefore the bounds here considered are more robust. We also show that dissipative effects are unimportant for a large spectrum of temperatures of the noise, while for low temperatures the excluded region in the parameter space is the more reduced, the lower the temperature.