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

Thursday, June 14, 2018 - 17:30
Donostia International Physics Center
Christian Schönenberger, Department of Physics, University of Basel, and Swiss Nanoscience Institute, Switzerland
Source Name: 

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

[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. Kłobus, 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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