**Quantum process tomography with coherent states**

A general quantum optical process can be fully characterized by injecting coherent states and performing optical homodyne tomography on the output states: nonclassical input states are surprisingly not required, even for nonclassical quantum processes [1,2]. As the Hilbert space is infinite dimensional, representations of states and processes must be regularized, e.g. truncated. I discuss and compare two of our approaches: a filtered Glauber–Sudarshan method vs a truncated Fock representation. Our method is applicable to multi-mode processes and to non-trace-preserving optical processes.\r\n[1] M. Lobino, D. Korystov, C. Kupchak, E. Figueroa, B. C. Sanders and A. I. Lvovsky, Complete characterization of quantum-optical processes, Science 322(5901): 563-566, 2008.\r\n[2] S. Rahimi-Keshari, A. Scherer, A. Mann, A. T. Rezakhani, A. I. Lvovsky and B. C. Sanders, Quantum process tomography with coherent states, New Journal of Physics 13: 013006 (17 pp.), 2011.\r\n