Constraints on dephasing widths and shifts in three-level quantum systems

It is shown that the density matrix equations for a three-level quantum system interacting with external radiation fields can lead to negative populations if arbitrary dephasing rates and shifts are included in these equations. To guarantee non-negative populations, the equations themselves impose c...

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Bibliographic Details
Published in:Physical review. A, Atomic, molecular, and optical physics Atomic, molecular, and optical physics, 2005-02, Vol.71 (2), Article 022501
Main Authors: Berman, P. R., O’Connell, Ross C.
Format: Article
Language:English
Subjects:
ATOMIC AND MOLECULAR PHYSICS
ATOMS
DENSITY MATRIX
ENERGY LEVELS
LINE WIDTHS
MARKOV PROCESS
PHOTON-ATOM COLLISIONS
RADIATION EFFECTS
SPECTRAL SHIFT
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Summary:It is shown that the density matrix equations for a three-level quantum system interacting with external radiation fields can lead to negative populations if arbitrary dephasing rates and shifts are included in these equations. To guarantee non-negative populations, the equations themselves impose certain restrictions on the dephasing widths and shifts. The constraints on the widths are shown to be identical to those that can be derived from a model of Markovian dephasing events, independent of any atom-field interaction.
ISSN:1050-2947
1094-1622
DOI:10.1103/PhysRevA.71.022501