We investigate experimentally the distribution of configurations of a ring with an elementary topological constraint, a ``figure-8'' twist. Using vibrated granular chains, which permit controlled preparation and direct observation of such a constraint, we show that configurations where one of the loops is tight and the second is large are strongly preferred. This agrees with recent predictions for equilibrium properties of topologically-constrained polymers. However, the dynamics of the tightening process weakly violate detailed balance, a signature of the nonequilibrium nature of this system.
@article{arxiv.cond-mat/0110612,
title = {Entropic Tightening of Vibrated Chains},
author = {M. B. Hastings and Z. A. Daya and E. Ben-Naim and R. E. Ecke},
journal= {arXiv preprint arXiv:cond-mat/0110612},
year = {2015}
}