The Physics Magazine featured a recent work from ITP III members Tobias Maier, Hans-Peter Büchler, and Nicolai Lang. The magazine's article "Quantum Materials Built from Scratch" summarizes for a broader audience the paper "Topological Order in Symmetric Blockade Structures":
Some experimental platforms (like arrays of atoms) facilitate the placement and coherent control of hundreds of elementary quantum systems that interact via simple two-body interactions. This opens the possibility of engineering quantum materials from scratch and motivates the “inverse problem” of quantum many-body physics: given a “toolbox” of microscopic constituents (like atoms) that can be placed freely and controlled precisely and that interact only via two-body interactions, is it possible to robustly engineer a prescribed quantum phase of matter—and if so, how—?
In the paper, we study this question for a toolbox that comprises elementary two-level systems (say atoms) that interact via a blockade mechanism: atoms separated by less than a given distance cannot be excited simultaneously. We assume that quantum fluctuations are induced by a uniform, coherent coupling between the two levels of the atoms.
Despite the simplicity of this toolbox, we systematically show how to engineer a many-body system that realizes the famous toric code topological order, a highly entangled quantum phase with potential applications for quantum computing. To do so, we introduce a particular type of symmetry that enforces strong quantum fluctuations and makes the ground state an equal-weight superposition of “loop configurations” of excitations. We then rigorously prove that this ground state has the sought-after topological order. This construction is interesting because it realizes an elusive quantum phase using only experimentally accessible two-body interactions.
In a broader sense, our results show how to incorporate quantum fluctuations systematically into the design process of artificial quantum materials.