arXiv subjects

Andreas Baumgartner

Publications and source records attributed to Andreas Baumgartner.

21 records · Page 2Linked to original sources

arXiv2014

Entanglement witnessing and quantum cryptography with non-ideal ferromagnetic detectors

We investigate theoretically the use of non-ideal ferromagnetic contacts as a mean to detect quantum entanglement of electron spins in transport experiments. We use a designated entanglement witness and find a minimal spin polarization of $η> 1/\sqrt{3} \approx 58 %$ required to demonstrate spin entanglement. This is significantly less stringent than the ubiquitous tests of Bell's inequality with $η> 1/\sqrt[4]{2}\approx 84%$. In addition, we discuss the impact of decoherence and noise on entanglement detection and apply the presented framework to a simple quantum cryptography protocol. Our results are directly applicable to a large variety of experiments.

cond-mat.mes-hall↗

arXiv2013

Non-local spectroscopy of Andreev bound states

We experimentally investigate Andreev bound states (ABSs) in a carbon nanotube quantum dot (QD) connected to a superconducting Nb lead (S). A weakly coupled normal metal contact acts as a tunnel probe that measures the energy dispersion of the ABSs. Moreover we study the response of the ABS to non-local transport processes, namely Cooper pair splitting and elastic co-tunnelling, that are enabled by a second QD fabricated on the same nanotube on the opposite side of S. We find an appreciable non-local conductance with a rich structure, including a sign reversal at the ground state transition from the ABS singlet to a degenerate magnetic doublet. We describe our device by a simple rate equation model that captures the key features of our observations and demonstrates that the sign of the non-local conductance is a measure for the charge distribution of the ABS, given by the respective Bogoliubov-de Gennes amplitudes $u$ and $v$.

cond-mat.mes-hall↗

arXiv2013

$g$-factor anisotropy in nanowire-based InAs quantum dots

The determination and control of the electron $g$-factor in semiconductor quantum dots (QDs) are fundamental prerequisites in modern concepts of spintronics and spin-based quantum computation. We study the dependence of the $g$-factor on the orientation of an external magnetic field in quantum dots (QDs) formed between two metallic contacts on stacking fault free InAs nanowires. We extract the $g$-factor from the splitting of Kondo resonances and find that it varies continuously in the range between $|g^*| = 5$ and 15.

cond-mat.mes-hall↗