Applied Physics B

, Volume 72, Issue 1, pp 35–42

Remarks on 2–q-bit states

  • B.-G. Englert
  • N. Metwally
Invited paper

DOI: 10.1007/s003400000502

Cite this article as:
Englert, BG. & Metwally, N. Appl Phys B (2001) 72: 35. doi:10.1007/s003400000502


We distinguish six classes of families of locally equivalent states in a straightforward scheme for classifying all 2–q-bit states; four of the classes consist of two subclasses each. The simple criteria that we stated recently for checking a given state’s positivity and separability are justified, and we discuss some important properties of Lewenstein–Sanpera decompositions. An upper bound is conjectured for the sum of the degree of separability of a 2–q-bit state and its concurrence.

PACS: 89.70.+c; 03.65.Bz

Copyright information

© Springer-Verlag 2000

Authors and Affiliations

  • B.-G. Englert
    • 1
  • N. Metwally
    • 3
  1. 1.Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, GermanyDE
  2. 2.Abteilung für Quantenphysik, Universität Ulm, Albert-Einstein-Allee 1, 89081 Ulm, GermanyDE
  3. 3.Sektion Physik, Universität München, Theresienstrasse 37, 80333 München, GermanyDE