Cooper-pair splitters as circuit elements for realizing topological superconductors

TL;DR

This paper introduces Y-splitter superconducting circuit elements that enable controlled interference and coherent propagation of split Cooper pairs, paving the way for realizing topological superconducting phases.

Contribution

It proposes a novel superconducting circuit element, the Y-splitter, and demonstrates how arrays of these can realize topological superconductors with nontrivial Chern numbers.

Findings

Y-splitters enable destructive interference of Cooper pairs.

Array configurations can host topological phases with Chern numbers ±2.

Experimental feasibility of the proposed circuits is discussed.

Abstract

Advances in materials and fabrication of superconducting devices allows the exploration of novel quantum effects in synthetic superconducting systems beyond conventional Josephson junction arrays. As an example, we introduce a new circuit element, the Y-splitter, a superconducting loop with three leads and three Josephson junctions, smaller or comparable in size to the superconducting coherence length of the material. By tuning magnetic flux through an array of Y-splitters, Cooper-pair transport can be made to interfere destructively, while spatially separated split Cooper pairs propagate coherently. We consider an array of Y-splitters connected in a two-dimensional star [Archimedean (3,$12^2$)] geometry, deformable into the kagome lattice, and find a rich phase diagram that includes topological superconducting phases with Chern numbers $\pm 2$. Experimental realization appears feasible.