Reduced density matrix identification of open quantum system

Identification of performance parameter of a multi-level open quantum system is a central problem in a growing number of applications of information engineering. Based on the quantum tomography, this paper aims at finding a method for identifying reduced density matrix of open quantum system. State identification of open quantum system approaches is presented for two-level, three-level and N-level systems, respectively. The results show that not only the reduced density matrix can be reestablished, but also the quantum state information can be received in quantum tomography experiment.