Spin-Weyl quantum unit: theoretical proposal

Abstract

We propose a four-state quantum system, or quantum unit, that can be realized in superconducting hetero-structures. The unit combines the states of a spin and an Andreev qubit providing the opportunity of quantum superpositions of their states. This functionality is achieved by tunnel coupling between a 4-terminal superconducting heterostucture housing a Weyl point, and a quantum dot. The quantum states in the vicinity of the Weyl point are extremely sensitive to small changes of superconducting phase, this gives reach opportunities for quantum manipulation. We establish an effective Hamiltonian for the setup and describe the peculiarities of the resulting spectrum. We concentrate on the 4-state subspace and explain how to make a double qubit in this setup. We review various ways to achieve quantum manipulation in the unit, this includes resonant, adiabatic, diabatic manipulation and combinations of those. We provide detailed illustrations of designing arbitrary quantum gates in the unit.

arXiv comment9 pages, 5 figures

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• Ground-state quantum geometry in superconductor-quantum dot chains
• A quantum interferometer for quartets in superconducting three-terminal Josephson junctions
• Proposal for detecting the $\pi -$shifted Cooper quartet supercurrent
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• Spintronics with a Weyl point in superconducting nanostructures
• Magnetointerferometry of multiterminal Josephson junctions
• Self-heating effects and switching dynamics in graphene multiterminal Josephson junctions
• Exploring the energy spectrum of a four-terminal Josephson junction: Towards topological Andreev band structures
• Multiterminal ballistic Josephson junctions coupled to normal leads
• Drastic effect of weak interaction near special points in semiclassical multiterminal superconducting nanostructures