Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 17: Quantum Manybody Systems (joint session QI/TT)

TT 17.9: Talk

Monday, March 9, 2026, 17:45–18:00, BEY/0245

Thermal Entanglement and Out-of-Equilibrium Thermodynamics in 1D Bosonic Systems — •Julia Mathe, Nicky Kai Hong Li, Pharnam Bakhshinezhad, and Giuseppe Vitagliano — TU Wien, Atominstitut, Stadionallee 2, 1020 Vienna, Austria

We investigate entanglement in- and out-of equilibirum in harmonic chains, with direct relevance to low-energy descriptions of paradigmatic models, like 1D Bose-Einstein condensates. Working in a regime where all states are Gaussian, we employ the logarithmic negativity and the covariance matrix criterion (CMC) as known entanglement quantifiers. For thermal states, we extensively characterize entanglement and its scaling behaviour, including in the massless (critical) limit. We extract the optimal entanglement witness coming from the CMC and uncover a simple mode-resolved structure underlying the entanglement-to-separability transition. At finite temperature, the optimal witnesses are diagonal in the normal-mode basis, allowing to characterize entanglement from a few normal mode uncertainties, which are physically related to static susceptibilities. We then investigate out-of-equilibrium dynamics arising from a time-dependent coupling and analyze entanglement growth, suppression, and transport. Based on this, we construct a full Gaussian framework for studying entanglement in thermodynamic cycles. Our results give a unified and physically intuitive picture of how entanglement emerges and evolves in 1D Gaussian many-body systems and show that thermal separability and entanglement are mainly governed by the low-energy (infrared) sector that also underlies the continuum field-theory description.

Keywords: harmonic chains; Gaussian quantum systems; thermal entanglement; out-of-equilibrium dynamics; Gaussian thermodynamic cycles