期刊
PHYSICAL REVIEW A
卷 88, 期 1, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevA.88.014302
关键词
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资金
- United States Army Research Office via the Defense Advanced Research Projects Agency-Optical Lattice Emulator program
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 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 et al., Phys. Rev. A 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.
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