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Domain Wall Control of Topological Qubits in the Kitaev SSH Chain

Griffith Rufo, Sabrina Rufo, Heron Caldas, Rosiane de Freitas

TL;DR

The paper introduces a Defected Kitaev–SSH Chain where a domain wall acts as a local switch that controls the presence and distribution of Majorana zero modes without leaving the topological phase. By tuning anisotropy and domain-wall strength, a solitonic Majorana mode binds at the wall and can redistribute zero modes between edges and the chain center, effectively turning a topological qubit on or off. This local control primitive enables parity-preserving operations, adiabatic qubit transport, and domain-wall networks for braiding-like readout, with robustness to finite chemical potential. The proposed approach reframes defects as actionable resources for topology-based quantum information processing and suggests scalable architectures where movable domain walls implement local qubit control and measurements.

Abstract

Zero energy states in one dimensional SSH Kitaev hybrid systems have emerged as promising candidates for topological qubits. In our work, we show that introducing a domain wall into a chain with anisotropic superconducting correlations provides a powerful way to control both the number and the nature of these boundary modes. The defect acts as a digital knob: its presence or absence flips the parity of zero modes and thus decides whether an isolated Majorana exists at the chain ends. This on/off mechanism is significantly more robust and simpler than fine-tuning global parameters such as chemical potential or hopping amplitudes. Moreover, anisotropy provides an additional lever to calibrate the effect of the defect, opening a pathway to architectures where topological qubits can be locally addressed by domain walls. This proposal reframes defects not as imperfections, but as useful resources for quantum information and computation.

Domain Wall Control of Topological Qubits in the Kitaev SSH Chain

TL;DR

The paper introduces a Defected Kitaev–SSH Chain where a domain wall acts as a local switch that controls the presence and distribution of Majorana zero modes without leaving the topological phase. By tuning anisotropy and domain-wall strength, a solitonic Majorana mode binds at the wall and can redistribute zero modes between edges and the chain center, effectively turning a topological qubit on or off. This local control primitive enables parity-preserving operations, adiabatic qubit transport, and domain-wall networks for braiding-like readout, with robustness to finite chemical potential. The proposed approach reframes defects as actionable resources for topology-based quantum information processing and suggests scalable architectures where movable domain walls implement local qubit control and measurements.

Abstract

Zero energy states in one dimensional SSH Kitaev hybrid systems have emerged as promising candidates for topological qubits. In our work, we show that introducing a domain wall into a chain with anisotropic superconducting correlations provides a powerful way to control both the number and the nature of these boundary modes. The defect acts as a digital knob: its presence or absence flips the parity of zero modes and thus decides whether an isolated Majorana exists at the chain ends. This on/off mechanism is significantly more robust and simpler than fine-tuning global parameters such as chemical potential or hopping amplitudes. Moreover, anisotropy provides an additional lever to calibrate the effect of the defect, opening a pathway to architectures where topological qubits can be locally addressed by domain walls. This proposal reframes defects not as imperfections, but as useful resources for quantum information and computation.

Paper Structure

This paper contains 11 sections, 4 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Model
  3. Localized zero energy states:
  4. Results and Conclusions
  5. Fine-tuning limit:
  6. Generic parameter regime:
  7. Applications for quantum computation:
  8. Encoding the qubit with Majorana parity:
  9. Qubit "on/off" via domain wall.
  10. Gates and readout (sketch).
  11. Conclusions

Figures (3)

  • Figure 1: Schematic representation of a spin--orbit--coupled nanowire deposited on top of two $s$-wave superconductors, for example, Al and Nb. An external magnetic field is applied along the wire, parallel to the superconducting surfaces.
  • Figure 2: Probability density $\rho_i = |\Psi_i|^2$ at site $i$ as a function of $\delta$ for $\mu = 0$. Results are shown for different values of the pairing ratio $\Delta_2/\Delta_1$: (a) $\Delta_2/\Delta_1 = 0.4$, (b) $\Delta_2/\Delta_1 = 0.6$, (c) $\Delta_2/\Delta_1 = 0.8$, and (d) Number of zero energy states as a function of $\delta$
  • Figure 3: Probability density $\rho_i = |\Psi_i|^2$ at site $i$ as a function of $\delta$ for $\mu = 1$. Results are shown for different values of the pairing ratio $\Delta_2/\Delta_1$: (a) $\Delta_2/\Delta_1 = 0.4$, (b) $\Delta_2/\Delta_1 = 0.6$, (c) $\Delta_2/\Delta_1 = 0.8$, and (d) $\Delta_2/\Delta_1 = 1.2$.