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Résumé |
I explore the dynamics of translationally invariant quantum spin-1/2 chains with local interactions and discrete
symmetries spontaneously broken at zero temperature. Starting from a setup where couplings between two
parts of the system are switched off, each part is prepared in independent equilibrium states, with one side
settling into a symmetry-breaking ground state. Upon reintroducing the couplings, time evolution generates a
front separating the ordered region. In integrable systems, this front recedes at the maximal velocity of
quasiparticle excitations over the ground state. I show that, generically, order parameters vary on a
subdiffusive scale of order $t^{1/3}$, with fluctuations exhibiting the same scaling. Thus, the interfacial
region is characterized by full-range correlations without cluster decomposition properties. Using the
transverse-field Ising chain as a case study, I show that all order parameters follow the same universal scaling
functions. Additionally, I present data on Rényi entanglement asymmetries and a prediction valid also in the
von Neumann limit. I introduce the Wigner-Yanase skew information to identify quantum contributions to the
variance of extensive observables. I reveal that the breakdown of cluster decomposition includes a quantum
contribution: subsystems within the interface, of extent comparable to the region, exist in macroscopic
quantum states. Finally, I outline a semiclassical approximation that proves particularly effective near the
edge of the lightcone. |
