Quantum Information Journal Club: “Symmetry-protected topology and deconfined solitons in a multi-link Z2 gauge theory”

Speaker: Enrico Calogero Domanti

Title: “Symmetry-protected topology and deconfined solitons in a multi-link Z2 gauge theory”

Venue&Time: Gray Room 3 / 11:30

Abstract: With the advent of quantum simulators, exploring exotic collective phenomena in lattice models with local symmetries and unconventional geometries is at reach of near-term experiments. Motivated by recent progress in this direction, we study a Z2 lattice gauge theory defined on a multi-graph with links that host Z2 gauge fields. Elementary Wilson loops along pairs of these bonds allow to identify a dynamical gauge-invariant flux, responsible for Aharonov-Bohm-like interference effects in the tunneling dynamics of charged matter residing on the vertices. We find inhomogeneous phases in which an ordered pattern of the gauge fluxes spontaneously breaks translational invariance. For an even number of links, this is caused by a phenomenon of dynamical Aharonov-Bohm caging, in which particles get trapped into portions of the lattice due to destructive interference. On the other hand, an odd number of links realizes a phenomenon analogous to the Peiels instability. In this case, long-range order is shown to coexist with symmetry protected topological order, which survives the quantum fluctuations of the gauge flux induced by an external electric field. Doping the system above half filling leads to the formation of topological soliton/anti-soliton pairs interpolating between different inhomogeneous orderings of the gauge fluxes. Quasiparticles carrying fractional charge and bound at the soliton centers emerge as deconfined degrees of freedom, as they can be arbitrarily separated without feeling a confining force, in spite of the long-range attractive interactions set by the small electric field on the individual integer charges.