  We have embedded an artificial atom, a superconducting "transmon" qubit, in
an open transmission line and investigated the strong scattering of incident
microwave photons ($\sim6$ GHz). When an input coherent state, with an average
photon number $N\ll1$ is on resonance with the artificial atom, we observe
extinction of up to 90% in the forward propagating field. We use two-tone
spectroscopy to study scattering from excited states and we observe
electromagnetically induced transparency (EIT). We then use EIT to make a
single-photon router, where we can control to what output port an incoming
signal is delivered. The maximum on-off ratio is around 90% with a rise and
fall time on the order of nanoseconds, consistent with theoretical
expectations. The router can easily be extended to have multiple output ports
and it can be viewed as a rudimentary quantum node, an important step towards
building quantum information networks.
