  We consider the Su-Schrieffer-Heeger (SSH) chain, which has 0, 1, or 2
topological edge states depending on the ratio of the hopping parameters and
the parity of the chain length. We couple a qubit to one edge of the SSH chain
and a semi-infinite undimerized chain to the other, and evaluate the dynamics
of the qubit. By evaluating the decoherence rate of the qubit we can probe the
edge states of the SSH chain. The rate shows strong even-odd oscillations with
the number of sites reflecting the presence or absence of edge states. Hence,
the qubit acts as an efficient detector of the topological edge states of the
SSH model. This can be generalized to other topological systems.
