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- Publisher
- American Physical Society (APS)
- Copyright
- ©2013 American Physical Society
- ISSN
- 1050-2947
- DOI
- 10.1103/PhysRevA.88.014302
- Publisher site
- See Article on Publisher Site
Abstract
Quantum discord is a measure of quantum correlation beyond entanglement. Computing quantum discord for simple quantum states is a basic problem. An analytical formula of quantum discord for two-qubit X states is first claimed in ( Ali , Rau , and Alber , Phys. Rev. A PLRAAN 1050-2947 10.1103/PhysRevA.81.042105 81 , 042105 ( 2010 ) ), but later found to be not always correct. I observe numerically that the formula is valid with worst-case absolute error 0.0021. For symmetric two-qubit X states, I give a counterexample to the analytical formula derived in ( F. F. Fanchini , Phys. Rev. A PLRAAN 1050-2947 10.1103/PhysRevA.81.052107 81 , 052107 ( 2010 ) ), but observe that the formula is valid with worst-case absolute error 0.0006. The formula has been used in many research papers. The results in all these works are approximately correct, even if they may not be exactly correct.
Journal
Physical Review A – American Physical Society (APS)
Published: Jul 18, 2013