We report an experimental demonstration of low-light-level photon switching by quantum interference in laser-cooled <sup>87</sup>Rb atoms. A resonant probe pulse with an energy per unit area of one photon per λ<sup>2</sup>/2π propagates through the optically thick atoms. Its energy transmittance is greater than 63%, or a loss of less than e<sup>−1</sup>, because of the effect of electromagnetically induced transparency. In the presence of a switching pulse with an energy per unit area of 1.4 photons per λ<sup>2</sup>/2π, the energy transmittance of the same probe pulse becomes less than 37%, or e<sup>−1</sup>. This substantial reduction of probe transmittance caused by switching photons may lead to potential applications in single-photon-level nonlinear optics and manipulation of quantum information.
© 2005 Optical Society of America
Yong-Fan Chen, Zen-Hsiang Tsai, Yu-Chen Liu, and Ite A. Yu, "Low-light-level photon switching by quantum interference," Opt. Lett. 30, 3207-3209 (2005)