We report the first experimental demonstration of a quantum controlled-NOT
gate for different photons, which is classically feed-forwardable. In the
experiment, we achieved this goal with the use only of linear optics, an
entangled ancillary pair of photons and post-selection. The techniques
developed in our experiment will be of significant importance for quantum
information processing with linear optics.Comment: 4 pages 4 figures, sumbitted to PR