  As is well known, qubits are the fundamental building blocks of quantum
computers, and more generally, of quantum information. A major challenge in the
development of quantum devices arises because the information content in any
quantum state is rather fragile, as no system is completely isolated from its
environment. Generally, such interactions degrade the quantum state, resulting
in a loss of information.
  Topological edge states are promising in this regard because they are in ways
more robust against noise and decoherence. But creating and detecting edge
states can be challenging. We describe a composite system consisting of a
two-level system (the qubit) interacting with a finite Su-Schrieffer-Heeger
chain (a hopping model with alternating hopping parameters) attached to an
infinite chain. In this model, the dynamics of the qubit changes dramatically
depending on whether or not an edge state exists. Thus, the qubit can be used
to determine whether or not an edge state exists in this model.
