1. Paradoxes of measures of quantum entanglement and Bell's inequality violation in two-qubit systems.
- Author
-
Maroulis, G., Bancewicz, T., Champagne, B., Buckingham, A.D., Miranowicz, Adam, Horst, Bohdan, and Koper, Andrzej
- Subjects
QUANTUM theory ,BELL'S theorem ,ENTROPY ,AMBIGUITY ,ROBUST control ,MONTE Carlo method ,PARADOX - Abstract
We review some counterintuitive properties of standard measures describing quantum entanglement and violation of Bell's inequality (often referred to as "nonlocality") in two-qubit systems. By comparing the nonlocality, negativity, concurrence, and relative entropy of entanglement, we show: (i) ambiguity in ordering states with the entanglement measures, (ii) ambiguity of robustness of entanglement in lossy systems and (iii) existence of two-qubit mixed states more entangled than pure states having the same negativity or nonlocality. To support our conclusions, we performed a Monte Carlo simulation of 10^6 two-qubit states and calculated all the entanglement measures for them. Our demonstration of the relativity of entanglement measures implies also how desirable is to properly use an operationally-defined entanglement measure rather than to apply formally-defined standard measures. In fact, the problem of estimating the degree of entanglement of a bipartite system cannot be analyzed separately from the measurement process that changes the system and from the intended application of the generated entanglement. [ABSTRACT FROM AUTHOR]
- Published
- 2010