Katharina Laubscher
ContactDepartment of PhysicsUniversity of Basel Klingelbergstrasse 82 CH4056 Basel, Switzerland

Short CV
2018  present:  PhD student in the Condensed Matter Theory & Quantum Computing Group at the University of Basel, supervised by Prof. Dr. Jelena Klinovaja and Prof. Dr. Daniel Loss (QCQT Fellowship) 
2014  2017:  Master of Science in Physics, University of Basel 
Master's thesis: Universal quantum computation using a hybrid quantum double model, supervised by Dr. James Wootton and Prof. Dr. Daniel Loss  
2011  2014:  Bachelor of Science in Physics, University of Basel 
Research interests
Majorana fermions and parafermions in condensed matter systems, topological quantum computationPublications
Show all abstracts.1.  Fractional Topological Superconductivity and Parafermion Corner States 
Katharina Laubscher, Daniel Loss, and Jelena Klinovaja. arXiv:1905.00885
We consider a system of weakly coupled Rashba nanowires in the strong spinorbit interaction (SOI) regime. The nanowires are arranged into two tunnelcoupled layers proximitized by a top and bottom superconductor such that the superconducting phase difference between them is π. We show that in such a system strong electronelectron interactions can stabilize a helical topological superconducting phase hosting Kramers partners of ℤ2m parafermion edge modes, where m is an odd integer determined by the position of the chemical potential. Furthermore, upon turning on a weak inplane magnetic field, the system is driven into a secondorder topological superconducting phase hosting zeroenergy ℤ2m parafermion bound states localized at two opposite corners of a rectangular sample. As a special case, zeroenergy Majorana corner states emerge in the noninteracting limit m=1, where the chemical potential is tuned to the SOI energy of the single nanowires.
 
2.  Universal quantum computation in the surface code using nonAbelian islands 
Katharina Laubscher, Daniel Loss, and James R. Wootton. Phys. Rev. A 100, 012338 (2019); arxiv:1811.06738.
The surface code is currently the primary proposed method for performing quantum error correction. However, despite its many advantages, it has no native method to faulttolerantly apply nonClifford gates. Additional techniques are therefore required to achieve universal quantum computation. Here we propose a new method, using small islands of a qudit variant of the surface code. This allows the nontrivial action of the nonAbelian anyons in the latter to process information stored in the former. Specifically, we show that a nonstabilizer state can be prepared, which allows universality to be achieved.
 
3.  Poking holes and cutting corners to achieve Clifford gates with the surface code 
Benjamin J. Brown, Katharina Laubscher, Markus S. Kesselring, and James R. Wootton. Phys. Rev. X 7, 021029 (2017); arXiv:1609.04673.
The surface code is currently the leading proposal to achieve faulttolerant quantum computation. Among its strengths are the plethora of known ways in which faulttolerant Clifford operations can be performed, namely, by deforming the topology of the surface, by the fusion and splitting of codes and even by braiding engineered Majorana modes using twist defects. Here we present a unified framework to describe these methods, which can be used to better compare different schemes, and to facilitate the design of hybrid schemes. Our unification includes the identification of twist defects with the corners of the planar code. This identification enables us to perform singlequbit Clifford gates by exchanging the corners of the planar code via code deformation. We analyse ways in which different schemes can be combined, and propose a new logical encoding. We also show how all of the Clifford gates can be implemented with the planar code without loss of distance using code deformations, thus offering an attractive alternative to ancillamediated schemes to complete the Clifford group with lattice surgery.
