2013/06/30 by Yichen Huang · 140 citations
Computer Science · Mathematics · Physics and Astronomy · #Computer science #Counterexample #Discrete mathematics #Mathematical physics #Mathematics #Measure (data warehouse) #Physics #Quantum #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum Mechanics and Applications #Quantum algorithm #Quantum correlation #Quantum discord #Quantum entanglement #Quantum mechanics #Qubit #Simple (philosophy) #quant-ph
paper · pdf · doi:10.1103/physreva.88.014302
published in Physical Review A 88(1) (American Physical Society) · slightly revised; published version
openalex publication_date 2013/07/18 · arxiv created 2013/08/01 · arxiv updated 2013/08/02 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.