Bell Diagonal and Werner State Generation: Entanglement, Non-Locality, Steering and Discord on the IBM Quantum Computer

• Main Authors: Elias Riedel Gårding, Nicolas Schwaller, Chun Lam Chan, Su Yeon Chang, Samuel Bosch, Frederic Gessler, Willy Robert Laborde, Javier Naya Hernandez, Xinyu Si, Marc-André Dupertuis, Nicolas Macris
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Entropy
• Subjects: entanglement; entropy; non-locality; steering; discord; IBMQ
• Online Access: https://www.mdpi.com/1099-4300/23/7/797

We propose the first correct special-purpose quantum circuits for preparation of Bell diagonal states (BDS), and implement them on the IBM Quantum computer, characterizing and testing complex aspects of their quantum correlations in the full parameter space. Among the circuits proposed, one involves only two quantum bits but requires adapted quantum tomography routines handling classical bits in parallel. The entire class of Bell diagonal states is generated, and several characteristic indicators, namely entanglement of formation and concurrence, CHSH non-locality, steering and discord, are experimentally evaluated over the full parameter space and compared with theory. As a by-product of this work, we also find a remarkable general inequality between “quantum discord” and “asymmetric relative entropy of discord”: the former never exceeds the latter. We also prove that for all BDS the two coincide.