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arXiv:2606.05696

Information-Geometric Bound on the Robustness of Entanglement Generation

Zain H. Saleem

quant-phSubmitted Jun 4, 2026• Announced Jun 5, 2026• 0 citations
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Abstract

Entanglement generation is a central resource for quantum information processing, quantum networking, and quantum sensing. In practical implementations, however, entangling interactions are inevitably subject to uncertainty and fluctuations in the interaction strength. We investigate the robustness of entanglement generation in the presence of such imperfections and establish a direct connection between the robustness of entanglement generation and quantum Fisher information (QFI). For two interacting qubits, we show that the reduction in concurrence caused by fluctuations in the interaction parameter is bounded by the QFI with respect to the interaction strength.

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Entanglement generation is a central resource for quantum information processing, quantum networking, and quantum sensing. In practical implementations, however, entangling interactions are inevitably subject to uncertainty and fluctuations in the interaction strength. We investigate the robustness of entanglement generation in the presence of such imperfections and establish a direct connection between the robustness of entanglement generation and quantum Fisher information (QFI). For two interacting qubits, we show that the reduction in concurrence caused by fluctuations in the interaction parameter is bounded by the QFI with respect to the interaction strength.
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Abstract We provide a quantitative analysis of the connection between entanglement measures and Maximized Quantum Fisher Information (MQFI) using extensive numerical analysis of 20,000 randomly generated two-qubit states. Our systematic study reveals strong empirical relationships between the metrological capacity of quantum states and three entanglement measures: concurrence, negativity, and relative entropy of entanglement. Optimization over local unitary transformations produces substantially more predictable relationships than fixed-generator approaches, as confirmed by bootstrap resampling, systematic data binning, and multiple model comparisons. Exponential fits reach R 2 > 0.99 and polynomial models achieve R 2 = 0.999, providing thorough empirical support for saturation behavior in quantum metrological advantage. Even separable states possess robust metrological utility (MQFI/4 ≈ 0.19, p < 0.0001), achieving approximately 19% of maximal Bell-state sensing capacity—confirming the importance of quantum coherence and discord beyond entanglement. Entanglement–metrology relationships remain stable under realistic decoherence, particularly phase damping. Our findings empirically validate predictions from quantum resource theory, establish empirical bounds for quantum sensor optimization, and offer direct practical guidance for the design of quantum sensing protocols.
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Entanglement measures such as concurrence, negativity and REE are well-known tools for quantifying non-classical correlations in quantum systems. However, these measures can lead to different state orderings for non-maximally entangled states. On the other hand, Quantum Fisher Information (QFI), while not an entanglement measure, provides a framework for analyzing a state's metrological potential. In this study, we numerically analyze the relationship between these entanglement measures and QFI for a large ensemble of random two-qubit states. We specifically focus on the maximized QFI (MQFI) obtained through local unitary rotations. Our findings demonstrate a strong correlation between entanglement and a state's metrological capacity, confirming that entanglement is a valuable resource. We show that while a state's QFI with a fixed generator can vary widely for a given entanglement value, local optimization to find the MQFI leads to a tighter, more predictable relationship. Our results also reinforce the principle that the metrological performance of all mixed states is fundamentally bounded by the theoretical limit of pure states. The polynomial fit equations for the upper and lower bounds of our data provide a quantitative description of these complex relationships.
We investigate the response of entanglement to temperature variations in interacting two-qubit thermal states. For a general two-qubit interaction Hamiltonian, we derive exact expressions for the thermal concurrence, its first and second derivatives with respect to inverse temperature, and the thermal quantum Fisher information. We show that the rate of change of thermal entanglement is bounded by the thermal quantum Fisher information. We further derive a bound relating entanglement curvature and thermal quantum Fisher information, and show that temperature uncertainty induces a loss of entanglement bounded by the same quantity that determines thermometric sensitivity. These results establish thermal quantum Fisher information as a fundamental constraint on the response and robustness of entanglement in interacting two-qubit thermal states.
We derive a universal upper bound on the speed of multipartite entanglement generation. For arbitrary differentiable pure multipartite states undergoing parameter-dependent evolution, we prove that the rate of change of generalized concurrence is bounded by the square root of the quantum Fisher information (QFI). The proof follows directly from the symmetric logarithmic derivative formalism, revealing the bound as a consequence of quantum estimation theory, while a complementary Schmidt-spectrum analysis identifies the conditions for saturation and yields a tighter bound for rank-two bipartitions. We illustrate these results in interacting many-body spin models and investigate their behavior across the quantum phase transition of the transverse-field Ising model. At the critical point, we find that the QFI can be strongly enhanced while the generalized concurrence is nearly stationary and its sensitivity to the coupling is suppressed. This demonstrates that the enhanced parameter sensitivity associated with quantum criticality need not arise from rapid changes in the magnitude of multipartite entanglement.