Entanglement in dual unitary quantum circuits with impurities

• URL: http://arxiv.org/abs/2410.03442v2
• Date: Fri, 08 Nov 2024 08:28:51 GMT
• Title: Entanglement in dual unitary quantum circuits with impurities
• Authors: Shachar Fraenkel, Colin Rylands,
• Abstract summary: We investigate entanglement dynamics in a quantum circuit perturbed by an impurity. We compute entanglement entropy for both a semi-infinite and a finite subsystem within a finite distance of the impurity. We show that such non-monotonic behavior can arise even in random chaotic circuits.
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• Abstract: Bipartite entanglement entropy is one of the most useful characterizations of universal properties in a many-body quantum system. Far from equilibrium, there exist two highly effective theories describing its dynamics -- the quasiparticle and membrane pictures. In this work we investigate entanglement dynamics, and these two complementary approaches, in a quantum circuit model perturbed by an impurity. In particular, we consider a dual unitary quantum circuit containing a spatially fixed, non-dual-unitary impurity gate, allowing for differing local Hilbert space dimensions to either side. We compute the entanglement entropy for both a semi-infinite and a finite subsystem within a finite distance of the impurity, comparing exact results to predictions of the effective theories. We find that for a semi-infinite subsystem, both theories agree with each other and the exact calculation. For a finite subsystem, however, both theories qualitatively differ, with the quasiparticle picture predicting a non-monotonic growth in contrast to the membrane picture. We show that such non-monotonic behavior can arise even in random chaotic circuits, pointing to a hitherto unknown shortcoming of the membrane picture in describing such systems.

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