The 8-cm-long silica-on-silicon photonic chip in the center of the picture served as the 4-photon QBSM (see figure 3B in the manuscript). Arrays of single-mode fibers are glued to the left and right sides of the chip. For viewing purposes, a red laser is coupled into two of the single mode fibers (right side of picture), which illuminate a portion of the on-chip interferometric network. For the boson sampling experiment, the red laser was replaced with single photon sources. There are five thermal phase shifting elements on top of the chip, though they were not used in this experiment. This image relates to a paper that appeared in the Dec. 20, 2012, issue of Science Express, published by AAAS. The paper, by Justin Spring at University of Oxford in Oxford, UK, and colleagues was titled, "Boson Sampling on a Photonic Chip."