Eur. Phys. J. D (2021) 75: 65
https://doi.org/10.1140/epjd/s10053-021-00055-1

Regular Article - Quantum Information

Any two-qubit state has nonzero quantum discord under global unitary operations

¹ Department of Mathematics, Government Girls’ General Degree College, 700023, Ekbalpore, Kolkata, India
² Department of Mathematics, Balagarh Bijoykrishna Mahavidyalaya, 712501, Balagarh, Dist. - Hooghly, India
³ Department of Mathematics, The Heritage College, 700107, Anandapur, Kolkata, India

^a kaushiki_mukherjee@rediffmail.com

Received: 3 October 2020
Accepted: 18 January 2021
Published online: 17 February 2021

Abstract

Quantum discord is significant in analyzing quantum nonclassicality beyond the paradigm of entanglement. Presently, we have explored the effectiveness of global unitary operations in manifesting quantum discord from a general two-qubit zero discord state. Apart from the emergence of some obvious concepts such as absolute classical-quantum and absolute quantum-classical states, more interestingly, it is observed that set of states characterized by absoluteness contains only maximally mixed state. Consequently, this marks the peak of effectiveness of global unitary operations in purview of manifesting nonclassicality from arbitrary two-qubit state when other standard methods fail to do so. A set of effective global unitaries has been provided in this context. Our observations have direct implications in remote state preparation task.