Disorder protected and induced local zero-modes in longer-range Kitaev chains

• Published in: Physical review. B 2018-10, Vol.98 (13), p.134507, Article 134507
• Main Authors: Lieu, Simon, Lee, Derek K. K., Knolle, Johannes
• Format: Article
• Language: English
• Subjects: Chains; Mathematical models; Phase diagrams; Quantum entanglement
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.98.134507

We study the effects of disorder on a Kitaev chain with longer-range hopping and pairing terms which is capable of forming local zero energy excitations and, hence, serves as a minimal model for localization-protected edge qubits. The clean phase diagram hosts regions with 0, 1, and 2 Majorana zero-modes (MZMs) per edge. Using a semianalytic approach corroborated by numerical calculations of the entanglement degeneracy, we show how phase boundaries evolve under the influence of disorder. While in general the 2 MZM region is stable with respect to moderate disorder, stronger values drive transition towards the topologically trivial phase. We uncover regions where the addition of disorder induces local zero-modes absent for the corresponding clean system. Interestingly, we discover that disorder destroys any direct transition between phases with zero and two MZMs by creating a tricritical point at the 2-0 MZM boundary of the clean system. Finally, motivated by recent experiments, we calculate the characteristic signatures of the disorder phase diagram as measured in dynamical local and nonlocal “qubit” correlation functions. Our work provides a minimal starting point to investigate the coherence properties of local qubits in the presence of disorder.