B. Mehmani, A. E. Allahverdyan, Th. M. Nieuwenhuizen
Published 2007-08-14, updated 2008-01-31Version 3
The density matrix of a two-level system (spin, atom) is usually determined by measuring the three non-commuting components of the Pauli vector. This density matrix can also be obtained via the measurement data of two commuting variables, using a single apparatus. This is done by coupling the two-level system to a mode of radiation field, where the atom-field interaction is described with the Jaynes--Cummings model. The mode starts its evolution from a known coherent state. The unknown initial state of the atom is found by measuring two commuting observables: the population difference of the atom and the photon number of the field. We discuss the advantages of this setup and its possible applications.
Comments: 7 pages, 8 figure, Phys. Rev. A
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