Manipulating topology in tailored artificial graphene nanoribbons

Topological phases of matter give rise to exotic physics that can be leveraged for next generation quantum computation^1,2 and spintronic devices^3,4.  Thus, the search for topological phases and the quantum states that they exhibit have become the subject of a massive research effort in condensed matter physics.  Topologically protected states have been produced in a variety of systems, including artificial lattices^6,7, graphene nanoribbons (GNRs)^8,9 and bismuth bilayers¹⁰.  Despite these advances, the real-time manipulation of individual topological states and their relative coupling, a necessary feature for the realization of topological qubits, remains elusive.  Guided by first-principles calculations, we spatially manipulate robust, zero-dimensional topological states by altering the topological invariants of quasi-one-dimensional artificial graphene nanostructures.  This is achieved by positioning carbon monoxide molecules on a copper surface to confine its surface state electrons into artificial atoms positioned to emulate the low-energy electronic structure of graphene derivatives.  Ultimately, we demonstrate control over the coupling between adjacent topological states that are finely engineered and simulate complex Hamiltonians.  Our atomic synthesis gives access to nanoribbon geometries beyond the current reach of synthetic chemistry, and thus provides an ideal platform for the design and study of novel topological and quantum states of matter.

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