Research: Circumventing quantum phase transitions in the preparation of topological states

Realizing low-temperature states of topological quantum matter has remained an outstanding challenge in synthetic materials. By definition, such (nonsymmetry protected) topological phases cannot be attained without going through a phase transition in a closed system, largely preventing their preparation in coherent quantum dynamics.

To overcome this fundamental caveat, SFB 1143 quantum physicists at Dresden together with their collaborators from Innsbruck now propose and study an experimentally feasible protocol for preparing topological states such as Chern insulators. This protocol relies on coupling the target system to a conjugate system, so as to prepare a symmetry protected topological phase in an extended system by intermittently breaking the protecting symmetry. Finally, the decoupled conjugate system is discarded, thus projecting onto the desired topological state in the target system. By construction, this protocol may be immediately generalized to the class of invertible topological phases, characterized by the existence of an inverse topological order. These findings are illustrated with microscopic simulations on an experimentally realistic Chern insulator model of ultracold fermionic atoms in a driven spin-dependent hexagonal optical lattice.

F. Tonielli, J. C. Budich, A. Altland, S. Diehl,
Topological field theory far from equilibrium,
Phys. Rev. Lett. 124, 240404 (2020) (arXiv)