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arXiv:2206.11213

Topologically protected πππ-ring qubits

Forrester, Michael, Fedor Vasilievich Kusmartsev

Published Jun 22, 2022• 0 citations
arXivHTMLPDF

Abstract

The $π$-ring qubit array is described using quasiclassical approaches that are shown to be accurate and give clarity to the complex energy landscape of connected vortex qubits. Using the techniques, large arrays of Josephson junction systems can be designed, including phase shift devices. Herein, connected arrays of loops containing $π$ junctions are described. These techniques are useful for design of quantum computers based on superconducting technologies, hybrid quantum technologies and quantum networks.

DOI
10.48550/arxiv.2206.11213

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The πππ-ring qubit array is described using quasiclassical approaches that are shown to be accurate and give clarity to the complex energy landscape of connected vortex qubits. Using the techniques, large arrays of Josephson junction systems can be designed, including phase shift devices. Herein, connected arrays of loops containing πππ junctions are described. These techniques are useful for design of quantum computers based on superconducting technologies, hybrid quantum technologies and quantum networks.
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We propose a complete quantum computation process on a topologically protected Josephson junction array system, originally proposed by Ioffe and Feigel'man [Phys. Rev. B 66, 224503 (2002)]. Logical qubits for computation are encoded in the punctured array. The number of qubits is determined by the number of holes. The topological degeneracy is lightly shifted by tuning the flux along specific paths. We show how to perform both single-qubit and basic quantum-gate operations in this system, especially the controlled-NOT (CNOT) gate.
The superconducting phase qubit combines Josephson junctions into superconducting loops and defines one of the promising solid state device implementations for quantum computing. While conventional designs are based on magnetically frustrated superconducting loops, here we discuss the advantages offered by πππ-junctions in obtaining naturally degenerate two-level systems. Starting from a basic five-junction loop, we show how to construct degenerate two-level junctions and superconducting phase switches. These elements are then effectively engineered into a superconducting phase qubit which operates exclusively with switches, thus avoiding permanent contact with the environment through external biasing. The resulting superconducting phase qubits can be understood as the macroscopic analogue of the `quiet' s-wave-d-wave-s-wave Josephson junction qubits introduced by Ioffe {\it et al.} [Nature {\bf 398}, 679 (1999)].
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