TY - JOUR T1 - Attractive Photons in a Quantum Nonlinear Medium JF - Nature (London) Y1 - 2013 A1 - Ofer Firstenberg A1 - Thibault Peyronel A1 - Qi-Yu Liang A1 - Alexey V. Gorshkov A1 - Mikhail D. Lukin A1 - Vladan Vuletic VL - 502 U4 - 71 UR - http://dx.doi.org/10.1038/nature12512 ER -