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Abstract
Generation and manipulation of quantum entangled electrons is an important concept in quantum mechanics, and necessary for advances in quantum information processing; but not yet established in solid state systems. A promising device is a superconductor-two quantum dots Cooper pair splitter. Early nanowire based devices, while efficient, are limited in scalability and further electron manipulation. We demonstrate an optimized, high efficiency, CVD grown graphene-based Cooper pair splitter. Our device is designed to induce superconductivity in graphene via the proximity effect, resulting in both a large superconducting gap Δ = 0.5 meV, and coherence length ξ = 200 nm. The flat nature of the device lowers parasitic capacitance, increasing charging energy EC. Our design also eases geometric restrictions and minimizes output channel separation. As a result we measure a visibility of up to 86% and a splitting efficiency of up to 62%. This will pave the way towards near unity efficiencies, long distance splitting, and post-splitting electron manipulation.
Highlights
Generation and manipulation of quantum entangled electrons is an important concept in quantum mechanics, and necessary for advances in quantum information processing; but not yet established in solid state systems
In our Y-shape Cooper pair splitter we achieve a 100% larger value for α and a full order of magnitude larger than previously demonstrated in a T-shape quantum dots (QD) geometry with graphene[19]
Previous work utilizing carbon nanotubes and demonstrating near unity efficiency, speculated that the high efficiency was aided by the nanotube region directly under the central lead becoming superconducting via proximity[14]
Summary
Generation and manipulation of quantum entangled electrons is an important concept in quantum mechanics, and necessary for advances in quantum information processing; but not yet established in solid state systems. High efficiency Cooper pair splitting (CPS) devices have been made using the superconductor-two quantum dot design[10,11]. Such devices have been made using one dimensional nanowires or nanotubes with the central superconductor of Al in a T-shape[11,12,13,14,15], with reported efficiencies of up to 90%14. Cooper pair splitting in graphene quantum dots (QD) coupled to a conventional-narrow superconducting wire has recently been demonstrated[19] In this T-shape design (essentially equivalent to the nanowire based devices) the spatially separated QDs are partially covered by the superconducting Al wire, resulting in a small charging energy of just 80 μeV. We predict that by using ultra-clean graphene devices of the same design, near unity efficiency can be achieved
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