  Any optical quantum information processing machine would be comprised of
fully-characterized constituent devices for both single state manipulations and
tasks involving the interaction between multiple quantum optical states.
Ideally for the latter, would be an apparatus capable of deterministic optical
phase shifts that operate on input quantum states with the action mediated
solely by auxiliary signal fields. Here we present the complete experimental
characterization of a system designed for optically controlled phase shifts
acting on single-photon level probe coherent states. Our setup is based on a
warm vapor of rubidium atoms under the conditions of electromagnetically
induced transparency with its dispersion properties modified through the use of
an optically triggered N-type Kerr non-linearity. We fully characterize the
performance of our device by sending in a set of input probe states and
measuring the corresponding output via balanced homodyne tomography and
subsequently performing the technique of coherent state quantum process
tomography. This method provides us with the precise knowledge of how our
optical phase shift will modify any arbitrary input quantum state engineered in
the mode of the reconstruction.
