Spin-Weyl quantum unit: theoretical proposal

Abstract

We propose a four-state quantum system, or quantum unit, that can be realized in superconducting heterostructures. 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.

Spintronics with a Weyl point in superconducting nanostructures

“…We observe that the tunneling breaks isotropy near the Weyl point. This has been also noted in 36 where we have considered tunneling to/from a Weyl point nanostructure to discrete electron states. In the following, we will neglect the energy dependence of Γ u,v which is a common assumption for the tunneling at energies close to the Fermi energy.…”

Ground-state quantum geometry in superconductor-quantum dot chains

“…More recently, multiterminal Josephson junctions (MJJs) consisting of many superconducting terminals have been theoretically investigated and shown to exhibit topologically nontrivial physics [19][20][21][22][23][24][25][26][27][28][29][32][33][34]. In such multiterminal systems, topology emerges in the synthetic space of superconducting phases and the integervalued Chern number can manifest itself in a quantized transconductance between two terminals [22,[24][25][26][27][28][29][30][31].…”