Abstract Quantum discord captures nonclassical correlations beyond entanglement and plays a piv-otal role in quantum communication, computation, and thermodynamics. Traditionally defined via entropy-based asymmetries in mutual information, discord remains conceptually rich but operationally opaque particularly in noisy or mixed-state regimes where entanglement vanishes yet quantum advantage persists. In this work, we introduce a novel formulation of discord based on Measurement-Induced Coherence Transfer (MICT). Rather than quantifying information imbalance, MICT discord measures the coherence gained in subsystem A when a projective measurement is performed on subsystem B. This directional, coherence-centric perspective reframes discord as a physically observable transfer process, firmly grounded in the resource theory of quantum coherence. Numerical simulations on Werner states validate the framework and reveal strong basis sensitivity: computational-basis measurements yield vanishing discord, whereas Hadamard-basis measurements consistently produce maximal coherence. This sharp divergence from standard discord measures underscores the operational significance of measurement choice in coherence-aware protocols. Finally, we discuss experimental feasibility, showing that MICT discord can be estimated via standard quantum state tomography and coherence monotones. Our results position MICT discord as a practical diagnostic and a new lens for interpreting quantum correlations, with potential applications in coherence-based benchmarking, quantum thermodynamics, and noise-resilient communication protocols.
Abstract Quantum discord captures nonclassical correlations beyond entanglement and plays a piv-otal role in quantum communication, computation, and thermodynamics. Traditionally defined via entropy-based asymmetries in mutual information, discord remains conceptually rich but operationally opaque particularly in noisy or mixed-state regimes where entanglement vanishes yet quantum advantage persists. In this work, we introduce a novel formulation of discord based on Measurement-Induced Coherence Transfer (MICT). Rather than quantifying information imbalance, MICT discord measures the coherence gained in subsystem A when a projective measurement is performed on subsystem B. This directional, coherence-centric perspective reframes discord as a physically observable transfer process, firmly grounded in the resource theory of quantum coherence. Numerical simulations on Werner states validate the framework and reveal strong basis sensitivity: computational-basis measurements yield vanishing discord, whereas Hadamard-basis measurements consistently produce maximal coherence. This sharp divergence from standard discord measures underscores the operational significance of measurement choice in coherence-aware protocols. Finally, we discuss experimental feasibility, showing that MICT discord can be estimated via standard quantum state tomography and coherence monotones. Our results position MICT discord as a practical diagnostic and a new lens for interpreting quantum correlations, with potential applications in coherence-based benchmarking, quantum thermodynamics, and noise-resilient communication protocols.
Abstract Quantum discord has emerged as a resource that extends beyond entanglement, yet its operational role remains underexplored. In this work, we introduce the Measurement-Induced Coherence Transfer (MICT) framework as both a theoretical and experimental diagnostic for coherence transfer. The MICT-Discord analysis establishes thresholds, scaling behavior, and noise resilience, mapping the geometry of discord across entanglement and measurement parameters. Complementing this, the MICT-Benchmark validates these predictions on IBM Quantum hardware through teleportation, superdense coding, and QKD protocols. The comparative results between the simulator, the ideal state vector,and the hardware output reveal discord as a sensitive witness of backend stability and coherence degradation. Together, MICT-Discord and MICT-Benchmark provide a reproducible suite for evaluating quantum platforms, positioning Discord as a practical diagnostic tool. Future directions include multipartite discord (GHZ/W states), error correction primitives, dynamic circuits with feed-forward, and cross-architecture reproducibility.
Abstract Quantum correlations extend beyond entanglement and play a central role in quantum information. Quantum discord captures nonclassical correlations that can persist in separable states. We present the first systematic geometric and operational analysis of MICT-discord in two-qubit systems, integrating numerical validation, scaling laws, noise robustness, and resource geometry. We validate MICT-discord against analytic benchmarks, uncover distinct scaling for entangled versus separable classes, and identify a crossover regime where separable states exceed entangled ones in discord, challenging monotonic assumptions. Under depolarizing and amplitude-damping channels, MICT-discord shows channel-dependent resilience, highlighting potential utility for NISQ devices. In contrast, maximally entangled mixed states (MEMS) expose limitations where MICT-discord fails to detect correlations at low purity. Geometric resource analysis delineates the convex hull boundaries of separable states and reveals the clustering of entangled states in high-discordance regions, providing operational thresholds. Overall, MICT-discord emerges as a structured, coherence-sensitive measure with demonstrated strengths in scaling and noise scenarios, alongside clear limitations in mixed-state regimes. Our results establish a reproducible, geometry-informed framework for discord analysis and suggest practical pathways for resource classification and benchmarking in quantum.
Abstract Quantum discord has emerged as a robust diagnostic of nonclassical correlations beyond entanglement, particularly relevant for noisy intermediate-scale quantum (NISQ) devices. We present an experimental study of measurement-induced coherence-transfer (MICT) discord proxies implemented on IBM Quantum hardware and benchmarked against simulator results. Discord and coherence landscapes, collapse maps, fidelity maps, and histograms demonstrate that collapse domains remain identifiable despite gate errors and readout noise. Fidelity difference maps quantify deviations between hardware and simulator, while summary metrics establish reproducible benchmarks for discord/coherence suppression and resilience. These findings indicate that discord-related signatures persist as global, topology-informed features in the presence of realistic noise, positioning discord and measurement-induced coherence as practical diagnostics for NISQ benchmarking and quantum machine-learning pipelines.
Abstract Quantum correlations extend beyond entanglement and play a central role in quantum information. Quantum discord captures nonclassical correlations that can persist in separable states. We present the first systematic geometric and operational analysis of MICT-discord in two-qubit systems, integrating numerical validation, scaling laws, noise robustness, and resource geometry. We validate MICT-discord against analytic benchmarks, uncover distinct scaling for entangled versus separable classes, and identify a crossover regime where separable states exceed entangled ones in discord, challenging monotonic assumptions. Under depolarizing and amplitude-damping channels, MICT-discord shows channel-dependent resilience, highlighting potential utility for NISQ devices. In contrast, maximally entangled mixed states (MEMS) expose limitations where MICT-discord fails to detect correlations at low purity. Geometric resource analysis delineates the convex hull boundaries of separable states and reveals the clustering of entangled states in high-discordance regions, providing operational thresholds. Overall, MICT-discord emerges as a structured, coherence-sensitive measure with demonstrated strengths in scaling and noise scenarios, alongside clear limitations in mixed-state regimes. Our results establish a reproducible, geometry-informed framework for discord analysis and suggest practical pathways for resource classification and benchmarking in quantum.
Quantum discord is a measure of nonclassical correlations in quantum systems. While the bipartite version of quantum discord is experimentally well-studied, the multipartite version has never been convincingly measured. In this study, we experimentally investigate tripartite quantum discord using an NMR quantum information processor. Building on a theoretical framework for conditional projective measurements and quantum conditional mutual information, we quantify the tripartite quantum discord and its contributions in different three-qubit states such as the Greenberger-Horne-Zeilinger (GHZ) and Werner (W) states as well as classical mixtures of biseparable Bell states, and classical mixtures of product states. The experiments employed full quantum state tomography and temporal averaging to prepare mixed states, achieving fidelities exceeding 95%. Our results confirm that quantum discord persists even in the absence of entanglement, highlighting its utility as a broader indicator of quantum correlations. Furthermore, we validate the nonconvexity of discord, confirming that classical mixtures of zero-discord states can exhibit nonzero discord. This experimentally confirms that quantum discord does not fit into the framework of resource theory. This work establishes a robust methodology for measuring quantum discord, illuminating the structure and distribution of quantum correlations in multipartite systems.
Quantum discord quantifies nonclassical correlations beyond the standard classification of quantum states into entangled and unentangled. Although it has received considerable attention, it still lacks any precise interpretation in terms of some protocol in which quantum features are relevant. Here we give quantum discord its first information-theoretic operational meaning in terms of entanglement consumption in an extended quantum-state-merging protocol. We further relate the asymmetry of quantum discord with the performance imbalance in quantum state merging and dense coding.