Ergodiscord: An Operational and Distinct Notion of Quantumness of Correlations

Alimuddin, Mir; Chowdhury, Snehasish Roy; Patra, Ram Krishna; Ghosh, Subhendu B.; Tufarelli, Tommaso; Adesso, Gerardo; Banik, Manik

Abstract

Nonclassicality in composite quantum systems depicts several puzzling manifestations, with Einstein-PodolskyRosen entanglement, Schrödinger steering, and Bell nonlocality being the most celebrated ones. In addition to those, an unentangled quantum state can also exhibit nonclassicality, as evidenced from notions such as quantum discord and work deficit. In this work, we present a general framework for exploring quantumness of correlations in multipartite quantum states. By exploiting the different signatures reflected on observable quantities depending on whether subsystems of a composite systems are probed jointly or independently, we introduce an operational quantifier of nonclassicality, termed ergodiscord. As we show, this newly proposed quantifier faithfully captures nonclassicality in any bipartite quantum state, while being fundamentally distinct from the original quantum discord. Moreover, ergodiscord uncovers an intriguing phenomenon called ‘nonlocal energy locking’, where a useful form of energy (i.e. work) gets locked in correlations of nonclassical states. We also show that a mixed nonclassical state can lock more work than the maximally entangled state of the corresponding system, establishing an interesting super-additivity phenomenon of nonlocal energy locking. The present work may inspire novel designs of quantum energy storage devices by utilizing nonclassical correlations in composite quantum systems.

Citation

Alimuddin, M., Chowdhury, S. R., Patra, R. K., Ghosh, S. B., Tufarelli, T., Adesso, G., & Banik, M. (2025). Ergodiscord: An Operational and Distinct Notion of Quantumness of Correlations. Physical Review Research, 7, Article 023200. https://doi.org/10.1103/PhysRevResearch.7.023200

• Journal Article Type: Article
• Acceptance Date: Apr 29, 2025
• Online Publication Date: May 29, 2025
• Publication Date: May 29, 2025
• Deposit Date: May 12, 2025
• Publicly Available Date: May 12, 2025
• Journal: Physical Review Research
• Electronic ISSN: 2643-1564
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Article Number: 023200
• DOI: https://doi.org/10.1103/PhysRevResearch.7.023200
• Public URL: https://nottingham-repository.worktribe.com/output/48978876
• Publisher URL: https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.023200