Quantum logical gates operating on stored light
  An implementation is proposed of single qubit gates, e.g., phase, NOT, \sqrt{NOT} and Hadamard, operating on polarized photons and based on light storage. Instead of processing photons themselves, qubit transformations are performed on atomic excitations due to photon storage in a medium of atoms in the tripod configuration. 
K. Slowik, A. Raczynski, J. Zaremba and S. Zielinska-Kaniasty
quant-ph