The quantum mechanics of position measurement of a macroscopic object is typically inaccessible because of strong coupling to the environment and classical noise. Here we monitor a mechanical resonator subject to an increasingly strong continuous position measurement and observe a quantum mechanical backaction force that rises in accordance with the Heisenberg uncertainty limit. For our optically-based position measurements, the backaction takes the form of a fluctuating radiation pressure from the Poisson-distributed photons in the coherent measurement field, termed radiation pressure shot noise. We demonstrate a backaction force that is comparable in magnitude to the thermal forces in our system. Additionally, we observe a temporal correlation between fluctuations in the radiation force and in the position of the resonator.
@article{arxiv.1209.6334,
title = {Observation of Radiation Pressure Shot Noise on a Macroscopic Object},
author = {T. P. Purdy and R. W. Peterson and C. A. Regal},
journal= {arXiv preprint arXiv:1209.6334},
year = {2013}
}