We analyze the nonlinear optical response of a four-level atomic system driven into a tripod configuration. The large cross-Kerr nonlinearities that occurr in such a system are shown to produce nonlinear phase shift of order π. Such a substantial shift may be observed in a cold atomic gas in a magneto-optical trap where it coupl be fasibly exploited towards the realization of a polarization quantum phase gate. The experimental feasibility of such a gate is here examined in detail.
@article{arxiv.quant-ph/0310148,
title = {Polarization phase gate with a tripod atomic system},
author = {S. Rebic and D. Vitali and C. Ottaviani and P. Tombesi and M. Artoni and F. Cataliotti and R. Corbalan},
journal= {arXiv preprint arXiv:quant-ph/0310148},
year = {2009}
}