  Quantum technologies, holding the promise of exponentially superior
performance than their classical counterparts for certain tasks, have
consistently encountered challenges, including instability in quantum light
sources, quantum decoherence and vulnerability to losses that topological
photonics happens to adeptly address. Here, we theoretically put forth a
quantum Su-Schrieffer-Heeger-type chain designed to greatly enhance
single-photon blockade (single-PB) effect with topological protection. By
designing the deliberate coupling strengths, the quantum-level lattices take
the form of a one-dimensional array with a topological edge state in
single-excitation space and a two-dimensional square breathing lattice with
topological corner states in two-excitation space, resulting in enhanced
single-photon excitation and the suppression of two-photon transitions.
Therefore the second-order correlation function is diminished by up to two
orders of magnitude at the cavity resonance frequency, accompanied by stronger
brightness.Furthermore, the PB effect is robust to local perturbations in
cavity-qubit coupling and qubit frequency, benefitting from topological
protection.
