The Topological Classification of One-Dimensional Symmetric QuantumWalks

authored by
Christopher Cedzich, T. Geib, F. A. Grünbaum, C. Stahl, L. Velázquez, A. H. Werner, R. F. Werner

We give a topological classification of quantum walks on an infinite 1D lattice, which obey one of the discrete symmetry groups of the tenfold way, have a gap around some eigenvalues at symmetry protected points, and satisfy a mild locality condition. No translation invariance is assumed. The classification is parameterized by three indices, taking values in a group, which is either trivial, the group of integers, or the group of integers modulo 2, depending on the type of symmetry. The classification is complete in the sense that two walks have the same indices if and only if they can be connected by a norm-continuous path along which all the mentioned properties remain valid. Of the three indices, two are related to the asymptotic behavior far to the right and far to the left, respectively. These are also stable under compact perturbations. The third index is sensitive to those compact perturbations which cannot be contracted to a trivial one. The results apply to the Hamiltonian case as well. In this case, all compact perturbations can be contracted, so the third index is not defined. Our classification extends the one known in the translation- invariant case, where the asymptotic right and left indices add up to zero, and the third one vanishes, leaving effectively only one independent index. When two translation-invariant bulks with distinct indices are joined, the left and right asymptotic indices of the joined walk are thereby fixed, and there must be eigenvalues at 1 or -1 (bulk-boundary correspondence). Their location is governed by the third index. We also discuss how the theory applies to finite lattices, with suitable homogeneity assumptions.

Institute of Theoretical Physics
CRC 1227 Designed Quantum States of Matter (DQ-mat)
External Organisation(s)
University of California at Berkeley
Universidad de Zaragoza
University of Copenhagen
Annales Henri Poincaré
No. of pages
Publication date
Publication status
Peer reviewed
ASJC Scopus subject areas
Statistical and Nonlinear Physics, Nuclear and High Energy Physics, Mathematical Physics
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