Topological protection of coherence in disordered open quantum systems

We consider topological protection mechanisms in dissipative quantum systems in the presence of quenched disorder, with the intent to prolong the coherence time of a fiducial qubit. The qubit is part of a network of other qubits and dissipative cavities whose coupling parameters are tunable, such that topological edge states can be stabilized. The evolution of the fiducial qubit is entirely determined by a non-Hermitian Hamiltonian which thus emerges from a bona fide physical process. Even in the presence of disorder, a winding number W can be defined and evaluated in real space, as long as certain symmetries are preserved. Hence we can construct the topological phase diagrams of noisy open quantum models, such as the non-Hermitian disordered Su-Schrieffer-Heeger dimer model and a trimer model that includes longer-range couplings. For finite-size systems we find that there are precisely W modes localized at one end of the chain. In such topological phases the qubit's coherence lifetime is exponentially large in the system size. In the presence of competing disorder parameters, interesting reentrance phenomena of topologically nontrivial sectors are observed. This means that in certain parameter regions, increasing disorder drastically increases the coherence time of the fiducial qubit.

Automated summary

This study explores topological protection mechanisms in dissipative quantum systems in the presence of quenched disorder to extend the coherence time of a fiducial qubit. It is found that under certain symmetries, a winding number can be defined and evaluated even in the presence of disorder, allowing for the construction of topological phase diagrams. In the presence of competing disorder parameters, interesting reentrance phenomena of topologically nontrivial sectors are observed, where increasing disorder drastically increases the coherence time of the fiducial qubit in certain parameter regions.