Application of the uncertainty principle to conditional measurements is investigated, and found to be valid for measurements on separated sub-systems. In light of this, an apparent violation of the uncertainty principle obtained by Kim and Shih in their realization of Popper's experiment (quant-ph/9905039) is explained through analogy with a simple optical system.
@article{arxiv.quant-ph/0005063,
title = {Comment on "Experimental realization of Popper's experiment: Violation of the uncertainty principle?"},
author = {A. J. Short},
journal= {arXiv preprint arXiv:quant-ph/0005063},
year = {2007}
}