Christian Schönenberger, University of Basel

Highly efficient Cooper pair splitting using quantum dots

co-authors: J. Schindele (1), L. Hofstetter (1), S. Csonka (2), A. Baumgartner (1)

(1) Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
(2)Department of Physics, Budapest University of Technology and Economics, Budafoki u. 6, 1111 Budapest, Hungary

An elegant idea for the creation of entangled electrons in a solid-state device is to split Cooper pairs, which are in a spin singlet state, by coupling a superconductor to two parallel quantum dots (QDs) in a Y-junction geometry [1]. Such Cooper pair splitting (CPS) was successfully detected in recent transport experiments on devices based on InAs nanowires [2,3] and carbon nanotubes (CNTs) [4]. After reviewing these earlier experiments we present new experiments on a CNT based Cooper pair splitter device with low inter-dot tunnel coupling. We find an unprecedented splitting efficiency, often much larger than 50%, the upper limit in devices with large inter-dot coupling [5]. Such CPS rates allow us to investigate this effect as a function of a variety of external parameters. A high CPS efficiency is a prerequisite for Bell state measurements, a clear way of proving that Cooper pairs can be extracted coherently and lead to spatially separated entangled electron pairs.

Part of this work has been done in collaboration with Nano-Science Center, Niels Bohr Institute of the University of Copenhagen (J. Nygard’s group). We acknowledge funding from the Swiss NFS, NCCR-Nano, NCCR-QSIT, FP7-SE2ND and ERC-QUEST.

[1] Recher et al., Phys. Rev. B 63, 165314 (2001)
[2] Hofstetter et al., Nature 461, 960-963 (2009)
[3] Hofstetter et al., Phys. Rev. Lett. 107, 136801 (2011)
[4] Herrmann el al., Phys. Rev. Lett. 104, 026801 (2010)
[5] Burset et al., Phys. Rev. B 84, 115448 (2011)