Quantum Coherence Lab

Zumbühl Group


News from our Group

Template-assisted nanowire networks on arXiv!

Topological qubits based on Majorana fermions have the potential to revolutionize the emerging field of quantum computing by making information processing significantly more robust to decoherence. Nanowires (NWs) are a promising medium for hosting these kinds of qubits, though branched NWs are needed to perform qubit manipulations. Here we report gold-free templated growth of III-V NWs by molecular beam epitaxy using an approach that enables patternable and highly regular branched NW arrays on a far greater scale than what has been reported thus far. Friedl et al. ArXiv:1803.00647

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Edge state tunneling spectroscopy paper on arXiv!

One of the most intriguing and fundamental properties of topological materials is the correspondence between the conducting edge states and the gapped bulk spectrum. So far, it has been impossible to access the full evolution of edge states in a magnetic field with critical system parameters due to poor resolution, remnant bulk conductivity, or disorder. Here, we present a novel type of tunneling spectroscopy which allows us to track the center of mass edge state positions with great precision and which can discriminate even spatially overlapping states due to their differing momenta based on tunneling along an extended GaAs quantum wire with translational symmetry. This results in unprecedented spatial resolution of about 1 nm at Tesla fields, while keeping the driving bias in the low microV regime in linear response. Patlatiuk et al. arXiv:1802.03847.

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Master Project available

We are looking for a highly motivated master student who is interested in working on low temperature quantum transport experiments. The goal of those experiments is to utilize a new spectroscopy technique developed in our group with the aim to obtain the velocities of edge states in cleaved edge overgrown samples. For further information please refer to the following pdf document or contact Prof. Dr. Zumbühl and/or Taras Patlatiuk.

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Work on the European Microkelvin Platform (EMP) infrastructures proposal in Heidelberg

After hours of deliberations, changes and small-group work sessions, it's quite energizing to see the progress on the proposal achieved in the past three days in Heidelberg on the European Microkelvin Platform EMP!!

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Symmetry Breaking of the Persistent Spin Helix in Quantum Transport appeared on arXiv!

In this work, we show that the physics of the quantum corrections to the conductivity around the persistent spin helix symmetry point can be treated very similar to the case with weak spin-orbit (SO) coupling, where the small parameter is the deviation from the PSH point due to either the mismatch a-b of the Rashba a and Dresselhaus b linear terms or due to the cubic SO term b3. This similarity makes it possible to derive closed-form equation for the weak (anti)localization magnetoconductivity including all these SO terms, which turns out to be identical in form to the well-known Hikami-Larkin-Nagaoka expression, but is now reparametrized im terms of the small parameters a-b and b3. Further, we perform quantum transport experiments in the same PSH regime, and develop a reliable two-step method to extract all parameters from fits to the new expression, obtaining excellent agreement with other recent experiments. This provides experimental confirmation of the new theory, and helps advancing SO coupling towards a powerful resource in emerging quantum technologies. Weigele et al. arXiv:1801.05657.

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