Tuning the Topological θ -Angle in Cold-Atom Quantum Simulators of Gauge Theories

Abstract

The topological θ-angle in gauge theories engenders a series of fundamental phenomena, including violations of charge-parity (CP) symmetry, dynamical topological transitions, and confinement-deconfinement transitions. At the same time, it poses major challenges for theoretical studies, as it implies a sign problem in numerical simulations. Analog quantum simulators open the promising prospect of treating quantum many-body systems with such topological terms, but, contrary to their digital counterparts, they have not yet demonstrated the capacity to control the θ-angle. Here, we demonstrate how a tunable topological θ-term can be added to a prototype theory with U(1) gauge symmetry, a discretized version of quantum electrodynamics in one spatial dimension. As we show, the model can be realized experimentally in a single-species Bose-Hubbard model in an optical superlattice with three different spatial periods, thus requiring only standard experimental resources. Through numerical calculations obtained from the time-dependent density-matrix renormalization group method and exact diagonalization, we benchmark the model system, and illustrate how salient effects due to the θ-term can be observed. These include charge confinement, the weakening of quantum many-body scarring, as well as the disappearance of Coleman’s phase transition due to explicit breaking of CP symmetry. This work opens the door towards studying the rich physics of topological gauge-theory terms in large-scale cold-atom quantum simulators.4 MoreReceived 15 April 2022Revised 19 September 2022Accepted 26 September 2022DOI:https://doi.org/10.1103/PRXQuantum.3.040316Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasColor confinementColor deconfinementConfinementQuantum simulationPhysical Systems1-dimensional systemsBose gasesTechniquesBose-Hubbard modelDensity matrix renormalization groupExact diagonalizationGauge symmetriesLattice gauge theoryPerturbation theoryAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics