The surface of three-dimensional topological insulators (TIs) constitutes an intriguing system for hosting Majorana zero modes (MZMs) when rendered superconducting via the proximity effect. To study the peculiar role of MZMs and the accompanied $4\pi$-periodic energy-phase relation in TI-based Josephson junctions (JJs), we constructed a superconducting flux qubit out of a JJ based on ${\text{Sn}}_{0.02}{\text{Bi}}_{1.08}{\text{Sb}}_{0.9}{\text{Te}}_2\mathrm{S}$ (Sn-doped BSTS). In the vicinity of the qubit’s sweet spot, we obtained a two-tone spectrum that differed from that of a conventional flux qubit. The analysis employing different models suggests the existence of 4π-periodic supercurrents in the junction. The results support the fact that superconducting flux qubits incorporating TI-based JJs may serve as a potential platform for the detection and further braiding of MZMs.

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• Andreev bound states
• Anyons
• Quantum information with solid state qubits
• Quantum interference effects
• Superconducting RF
• Topolectrical circuits
• Superconducting qubits
• Topological insulators