Quasiparticle dynamics of symmetry-resolved entanglement after a quench: Examples of conformal field theories and free fermions

The time evolution of the entanglement entropy is a key concept to understand the structure of a nonequilibrium quantum state. In a large class of models, such evolution can be understood in terms of a semiclassical picture of moving quasiparticles spreading the entanglement throughout the system. However, it is not yet known how the entanglement splits between the sectors of an internal local symmetry of a quantum many-body system. Here, guided by the examples of conformal field theories and free-fermion chains, we show that the quasiparticle picture can be adapted to this goal, leading to a general conjecture for the charged entropies whose Fourier transform gives the desired symmetry-resolved entanglement ${S}_{n}(q)$. We point out two physically relevant effects that should be easily observed in atomic experiments: a delay time for the onset of ${S}_{n}(q)$ which grows linearly with $|\mathrm{\ensuremath{\Delta}}q|$ (the difference between the charge $q$ and its mean value) and an effective equipartition when $|\mathrm{\ensuremath{\Delta}}q|$ is much smaller than the subsystem size.

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