Research Highlights
Exact projected entangled pair ground states with topological invariant
Discovery of new exact topological tensor network states
Illustration of the projected entangled simplex state. The blue wiggly lines denote the initial state of virtual fermions (blue balls) entangled across hexagons. The transparent red balls denote the projection onto the physical fermions (red balls).
We report on a class of gapped projected entangled pair states (PEPS) with non-trivial Euler topology motivated by recent progress in band geometry. In the non-interacting limit, these systems have optimal conditions relating to saturation of quantum geometrical bounds, allowing for parent Hamiltonians whose lowest bands are completely flat and which have the PEPS as unique ground states. Protected by crystalline symmetries, these states evade restrictions on capturing tenfold-way topological features with gapped PEPS. These PEPS thus form the first tensor network representative of a non-interacting, gapped two-dimensional topological phase, similar to the Kitaev chain in one dimension. Using unitary circuits, we then formulate interacting variants of these PEPS and corresponding gapped parent Hamiltonians. We reveal characteristic entanglement features shared between the free-fermionic and interacting states with Euler topology. Our results hence provide a rich platform of PEPS models that have, unexpectedly, a finite topological invariant, forming the basis for new spin liquids, quantum Hall physics, and quantum information pursuits.
Exact projected entangled pair ground states with topological Euler invariant, Thorsten B. Wahl, Wojciech J. Jankowski, Adrien Bouhon, Gaurav Chaudhary, Robert-Jan Slager, Nature Communications 16, 284 (2025).