"DIPC Colloquium: Cooper-pairs are nice, but split ones too!"

Who: Christian Schönenberger, Department of Physics, University of Basel, and Swiss Nanoscience Institute, Switzerland

Place: Donostia International Physics Center

Date: Thursday, 14 June 2018, 17:30

An elegant concept for the creation of entangled electrons in a solid-state device is to split Cooper pairs by coupling a superconductor to two parallel quantum dots (QDs) in a Y-junction geometry [1]. Cooper pair splitting (CPS) was investigated in recent years in devices based on InAs nanowires [2,3] and carbon nanotubes (CNTs) [4,5] and identified by a positive correlation between the currents through the QDs. I will first review these experiments and demonstrate that high splitting efficiencies >90% can be achieved [5]. A high CPS efficiency is a prerequisite for Bell state measurements [6], a clear way of proving that Cooper pairs can be extracted coherently, leading to spatially separated entangled electron pairs. Further requirements on entanglement measurements will be addressed in the talk as well [6] and a future perspective will be given.

My aim is to give a historical view of research that started around 10 years ago in my lab, hopefully understandable a general audience interested in solid-state physics in general. This journey shows how scientific research evolves, where one often takes detours and where one constantly has to reflect the finding in the lab based on either physical intuition (simple minded models) or, if available, good theory.

This is a collaborative effort with many people, see my group website www.nanoelectronics.ch and other goups as well. I would like to mention in particular the groups of Szabolcs Csonka, Budapst University of Technology and Economy, Jesper Nygard, Nano-Science Center, Niels Bohr Institute of the University of Copenhagen, and Jan Martinek- IFM-PAN, Poznan, Polen. I acknowledge funding from the Swiss NFS, SNI, NCCR-QSIT, FP7-SE2ND and ERC-QUEST.

[1] P. Recher, E.V. Sukhorukov and D. Loss, Phys. Rev. B 63, 165314 (2001).
[2] L. Hofstetter, S. Csonka, J. Nygård and C. Schönenberger, Nature 461, 960 (2009).
[3] L. Hofstetter, S. Csonka, A. Baumgartner, G. Fülöp S. d'Hollosy, J. Nygård and C. Schönenberger, Phys. Rev. Lett. 107, 136801 (2011).
[4] L.G. Herrmann, F. Portier, P. Roche, A. Levy Yeyati, T. Kontos and C. Strunk, Phys. Rev. Lett. 104, 026801 (2010).
[5] J. Schindele, A. Baumgartner, and C. Schönenberger, Phys. Rev. Lett. 109, 157002 (2012).
[6] W. K?obus, A. Grudka, A. Baumgartner, D. Tomaszewski, C. Schönenberger, and J. Martinek, Phys. Rev. B 89, 125404 (2014).
[7] G. Fülöp, S. d'Hollosy, A. Baumgartner, P. Makk, V. A. Guzenko, M. H. Madsen, J. Nygård, C. Schönenberger, and S. Csonka, Phys. Rev. B 90, 235412 (2014).
[8] J. Schindele, A. Baumgartner, R. Maurand, M. Weiss, and C. Schönenberger, Phys. Rev. B 89, 045422 (2014).

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