Katharina Laubscher


Department of Physics
University of Basel
Klingelbergstrasse 82
CH-4056 Basel, Switzerland

email:view address

tel: +41 61 207 36 95

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 computation


Show all abstracts.

1.  Fractional Topological Superconductivity and Parafermion Corner States
Katharina Laubscher, Daniel Loss, and Jelena Klinovaja.

We consider a system of weakly coupled Rashba nanowires in the strong spin-orbit interaction (SOI) regime. The nanowires are arranged into two tunnel-coupled 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 electron-electron 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 in-plane magnetic field, the system is driven into a second-order topological superconducting phase hosting zero-energy ℤ2m parafermion bound states localized at two opposite corners of a rectangular sample. As a special case, zero-energy Majorana corner states emerge in the non-interacting 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 non-Abelian islands
Katharina Laubscher, Daniel Loss, and James R. Wootton.

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 fault-tolerantly apply non-Clifford 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 non-trivial action of the non-Abelian anyons in the latter to process information stored in the former. Specifically, we show that a non-stabilizer 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)

The surface code is currently the leading proposal to achieve fault-tolerant quantum computation. Among its strengths are the plethora of known ways in which fault-tolerant 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 single-qubit 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 ancilla-mediated schemes to complete the Clifford group with lattice surgery.