Coupling spin qubits via superconductors

TL;DR

This paper proposes a method to use superconductors for coupling, initializing, and reading out spatially separated spin qubits, leveraging crossed Andreev reflection to enable long-distance qubit interactions.

Contribution

It introduces a novel approach to couple spin qubits via superconductors, enabling long-range interactions and control using crossed Andreev reflection.

Findings

Superconductors can mediate coupling between distant spin qubits.

Crossed Andreev reflection induces a controllable singlet-triplet splitting.

Long-distance two-qubit coupling is achievable beyond the superconducting coherence length.

Abstract

We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially leaks into the superconductor via crossed Andreev reflection. This induces a gate-controlled singlet-triplet splitting which, with an appropriate superconductor geometry, remains large for dot separations within the superconducting coherence length. Furthermore, we show that when two double-dot singlet-triplet qubits are tunnel coupled to a superconductor with finite charging energy, crossed Andreev reflection enables a strong two-qubit coupling over distances much larger than the coherence length.