Comment on "Contextuality and quantum discord"

Abstract

In a paper, Al-Qasimi [Physics Letters A 449 (2022) 128347] proposed a criterion for contextuality of two-qubit systems extending Peres' proof of contextuality [Phys. Lett. A 151 (1990) 107]. Using this criterion, Al-Qasimi argued that certain discordant states can be contextual even if they are not entangled. Here I demonstrate that Al-Qasimi's criterion does not, in general, imply contextuality of two-qubit system. However, I point out that Al-Qasimi's criterion is related to a different notion of operational nonclassicality of discordant feature, which is inequivalent to contextuality. This nonclassicality beyond contextuality has been formalized in C. Jebarathinam and R. Srikanth [Int. J. Quantum Inf. 23 (2025) 2550037]. Identifying Al-Qasimi's criterion as demonstration of quantum correlation beyond contextuality, it then follows that Al-Qasimi's main conclusion that one cannot equate quantum correlation and discordant feature is made precise.