Journal of Russian Laser Research

, Volume 36, Issue 5, pp 430–439 | Cite as

Unitary Transform and Subadditivity Condition for Composite and Noncomposite Systems



We study quantum correlations on the example of a bipartite system of two qubits. The system is described by the density matrix corresponding either to the Werner state or a generic X state. Also we study an analogous density matrix for the single-qudit state of a four-level atom. We perform the global unitary transform, calculate the quantum mutual information, and investigate its dependence on the parameters of the unitary matrix. Also we discuss the process of transforming a separable state into the entangled state for the composite system of two qubits and a single qudit.


quantum entanglement Werner state X state quantum information 


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Moscow Institute of Physics and Technology (State University)Moscow RegionRussia
  2. 2.Lebedev Physical InstituteRussian Academy of SciencesMoscowRussia
  3. 3.Physics DepartmentTomsk State UniversityTomskRussia

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