Move aside, aluminum
Some of the most promising schemes for quantum information processing involve superconductors. In addition to the established superconducting qubits, topological qubits may one day be realized in semiconductor-superconductor heterostructures. The superconductor most widely used in this context is aluminum, in which processes that cause decoherence are suppressed. Pendharkar et al. go beyond this paradigm to show that superconducting tin can be used in place of aluminum (see the Perspective by Fatemi and Devoret). The authors grew nanowires of indium antimonide, which is a semiconductor, and coated them with a thin layer of tin without using cumbersome epitaxial growth techniques. This process creates a well-defined, “hard” superconducting gap in the nanowires, which is a prerequisite for using them as the basis for a potential topological qubit.
Improving materials used to make qubits is crucial to further progress in quantum information processing. Of particular interest are semiconductor-superconductor heterostructures that are expected to form the basis of topological quantum computing. We grew semiconductor indium antimonide nanowires that were coated with shells of tin of uniform thickness. No interdiffusion was observed at the interface between Sn and InSb. Tunnel junctions were prepared by in situ shadowing. Despite the lack of lattice matching between Sn and InSb, a 15-nanometer-thick shell of tin was found to induce a hard superconducting gap, with superconductivity persisting in magnetic field up to 4 teslas. A small island of Sn-InSb exhibits the two-electron charging effect. These findings suggest a less restrictive approach to fabricating superconducting and topological quantum circuits.
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