Quantum process tomography is a procedure by which an unknown quantum
operation can be fully experimentally characterized. We reinterpret Choi's
proof of the fact that any completely positive linear map has a Kraus
representation [Lin. Alg. and App., 10, 1975] as a method for quantum process
tomography. Furthermore, the analysis for obtaining the Kraus operators are
particularly simple in this method.Comment: submitted to special issue of JMP on QI