Quantum tomography as a tool for the characterization of optical devices

We describe a novel tool for the quantum characterization of optical devices. The experimental set-up involves a stable reference state that undergoes an unknown quantum transformation and is then revealed by balanced homodyne detection. Through tomographic analysis of the homodyne data we are able to characterize the signal and to estimate parameters of the interaction, such as the loss of an optical component or the gain of an amplifier. We present experimental results for coherent signals, with application to the estimation of losses introduced by simple optical components, and show how these results can be extended to the characterization of more general optical devices.