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In open quantum systems, pure-dephasing interactions naturally generate system-environment entanglement from initial coherences. While this qualitative effect is well known, quantifying the created entanglement under general mixed-state conditions remains theoretically challenging. In this seminar, I will present a lower bound and an upper bound on entanglement generation, measured by the relative entropy of entanglement, for arbitrary initial conditions. The lower-bound of entanglement is given by the initial relative entropy of coherence minus the residual uncertainty after an optimal environmental measurement. The upper-bound is using the decoherence strength,showing that larger entanglement yields more decoherence. For two-dimensional central systems, The lower bound gets simplified to a closed-formula where uncertainty on the environment is represented as the fidelity between environmental states. I will show plots demonstrating the analytical results using the spin-boson model , highlighting the real-time entanglement dynamics across the Markovian to non-Markovian crossover. This talk is based on my work [1].

References

[1]M. Takahashi and J. K. Korbicz (2025). Coherence-assisted entanglement activation during open evolution. Physical Review A 112, 032222.
[2]T. Baumgratz, M. Cramer, and M. B. Plenio (2014). Quantifying coherence. Phys. Rev. Lett. 113, 140401.
[3]A. Streltsov, U. Singh, H. S. Dhar, M. N. Bera, and G. Adesso (2015). Measuring quantum coherence with entanglement. Phys. Rev. Lett. 115, 020403.
[4]K. Roszak (2018). Criteria for system-environment entanglement generation for systems of any size in pure-dephasing evolutions. Phys. Rev. A 98, 052344.
[5]J.-D. Lin, P.-W. Tu, K.-Y. Lee, N. Lambert, A. Miranowicz, F. Nori, and Y.-N. Chen (2025). Resource efficient certification of system environment entanglement solely from reduced system dynamics. arXiv preprint arXiv:2510.17140.