Long-range exchange interaction between spin qubits mediated by a superconducting link at finite magnetic field

Abstract

Solid state spin qubits are promising candidates for the realization of a quantum computer due to their long coherence times and easy electrical manipulation. However, spin-spin interactions, which are needed for entangling gates, have only limited range as they generally rely on tunneling between neighboring quantum dots. This severely constrains scalability. Proposals to extend the interaction range generally focus on coherent electron transport between dots or on extending the coupling range. Here, we study a setup where such an extension is obtained by using a superconductor as a quantum mediator. Because of its gap, the superconductor effectively acts as a long tunnel barrier. We analyze the impact of spin-orbit (SO) coupling, external magnetic fields, and the geometry of the superconductor. We show that while spin non-conserving tunneling between the dots and the superconductor due to SO coupling does not affect the exchange interaction, strong SO scattering in the superconducting bulk is detrimental. Moreover, we find that the addition of an external magnetic field decreases the strength of the exchange interaction. Fortunately, the geometry of the superconducting link offers a lot of room to optimize the interaction range, with gains of over an order of magnitude from a 2D film to a quasi-1D strip. We estimate that for superconductors with weak SO coupling (\textit{e.g.}, aluminum) exchange rates of up to 100\,MHz over a micron-scale range can be achieved with this setup in the presence of magnetic fields of the order of 100\,mT.

References in corpus (8)

• Supplementary information for "Quantum supremacy using a programmable superconducting processor"
• Demonstration of Entanglement of Electrostatically Coupled Singlet-Triplet Qubits
• Prospects for Spin-Based Quantum Computing
• Strong Coupling of a Single Electron in Silicon to a Microwave Photon
• Hybrid superconductor-semiconductor devices made from self-assembled SiGe nanocrystals on silicon
• Long-range entanglement for spin qubits via quantum Hall edge modes
• Fermi-liquid effects in the gapless state of marginally thin superconducting films
• Weak localization corrections to the thermal conductivity in $s$-wave superconductors

Cited by in corpus (6)

• Controlled crossed Andreev reflection and elastic co-tunneling mediated by Andreev bound states
• High-fidelity two-qubit gates of hybrid superconducting-semiconducting singlet-triplet qubits
• Coupled superconducting spin qubits with spin-orbit interaction
• Fabry-Perot superconducting diode
• A flux-controlled two-site Kitaev chain
• Spin-resolved nonlocal transport in proximitized Rashba nanowires