du 26 novembre 2021 au 27 novembre 2021
Publié le 23 novembre 2021 Mis à jour le 23 novembre 2021

Séminaire de Maurizio Fagotti

Séminaire
Séminaire

Quantum Quenches after Localised Perturbations.

Vendredi 26 novembre, 13h00 (en distanciel sur Microsoft Teams) ( Séminaire de matière condensée )

Quantum Quenches after Localised Perturbations.

Maurizio FAGOTTI
(CNRS - LPTMS)

I consider two distinct examples in which a localised perturbation to the state affects the long-time limit in a macroscopic way.
In the first example I describe the effect of perturbations in quantum jammed states. These are states  where  the  phase  space available  to  particles shrinks to zero, an interpretation quite accurate in integrable systems, where stable quasiparticles scatter elastically. I focus on the dual folded XXZ model, which is an integrable model equivalent to the Heisenberg XXZ spin-1/2 chain in the limit of large anisotropy. Besides pointing out the memory effects after a jamming-breaking localised measurement, I show that a charge  density  can become a nontrivial function of the ratio between distance and time notwithstanding the corresponding current approaching zero.
In the second example I consider time evolution from a more conventional initial state. Specifically, I investigate the effect of a single spin flip preceding a global quench. Notwithstanding the final (local) Hamiltonian being equivalent to the XYZ Heisenberg one, the effect of the localised perturbation does not fade away however large the distance from the perturbation is. In particular, translational invariance is not restored and the infinite time limit depends on whether the spin was flipped or not. I argue that this phenomenon is more general than the particular example considered and conjecture that it is triggered by topological properties, specifically, the existence of “semilocal charges”.

References:
[1] K Bidzhiev, MF, and L Zadnik, "Macroscopic effects of localised measurements in jammed states of quantum spin chains", arXiv:2108.03230
[2] L Zadnik, S Bocini, K Bidzhiev, and MF, "Measurement catastrophe and ballistic spread of charge density with vanishing current", arXiv:2111.06325
[3] MF, "Global Quenches after Localised Perturbations", arXiv:2110.11322


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