Momentum diffusion is a possible mechanism for driving macroscopic quantum systems towards classical behaviour. Experimental tests of this hypothesis rely on a precise estimation of the strength of this diffusion. We show that quantum-mechanical squeezing offers significant improvements, including when measuring position. For instance, with 10dB of mechanical squeezing, experiments would require a tenth of proposed free-fall times. Momentum measurement is better by an additional factor of three, while another quadrature is close to optimal. These have particular implications for the space-based MAQRO proposal -- where it could rule out the spontaneous collapse theory due to Ghirardi, Rimini, and Weber -- as well as terrestrial optomechanical sensing.
@article{arxiv.1901.02497,
title = {Quantum enhanced estimation of diffusion},
author = {Dominic Branford and Christos N. Gagatsos and Jai Grover and Alexander J. Hickey and Animesh Datta},
journal= {arXiv preprint arXiv:1901.02497},
year = {2020}
}