INFERRING THE DENSITY-MATRIX FOR A SYSTEM OF AN UNKNOWN HAMILTONIAN

An approximate inference approach is advanced in order to determine th e density matrix in cases in which the pertinent Hamiltonian is unknow n, and the available expectation values pertain to noncommuting observ ables. The inference of both pure and mixed states is addressed, and o n an equal footing, without facing infinities in the pure state limit. Information-theoretical tools are employed.