Quantum technology

Research areas:

• Generating, manipulating and detecting electronic entanglement in mesoscopic and nanoscale systems
• Superconductor-semiconductor hybrid structure for quantum technologies. 

Generating, manipulating and detecting electronic entanglement in mesoscopic and nanoscale systems.

This effort comprises theoretical research in e.g. orbital entanglement and Bell inequalities in hybrid superconducting systems, entanglement from two-particle interference with edge states in quantum Hall conductors, sub-decoherence time generation and detection of entanglement in quantum dot systems and minimal entanglement witnessing with current correlations. In addition, the pumping of pairs of entangled electrons and entangled state tomography with current cross-correlations have been investigated. The focus in all works has been on two-electron entanglement and detection with experimentally available low-frequency electrical current cross-correlations. The ongoing and planned investigations on the topic concern non-linear entanglement witnesses and deterministic, on-demand generation of pairs of entangled electrons.

Superconductor-semiconductor hybrid structure for quantum technologies.

We theoretically investigate different ways of exploiting superconducting proximity effect in semiconductors for fundamental physics experiments and for quantum technologies. One activity is within topological superconductivity and Majorana bound states in hybrid superconductor-semiconductor structures, for example in chain of quantum dots coupled via narrow superconducting regions. The main focus of the theoretical work at NanoLund is now to guide and steer our experimental collaborators as they attempt first proof of principle experiments to reveal the unique properties of topological quantum states and their use in quantum information processing. We also investigate how coupling semiconductors and superconductors can provide additional functionality in other (nontopological) quantum technologies, for example to couple spin qubits over large distances, in gate-controlled superconducting qubits, and in new types of qubits based on Andreev bound states.

Topological superconductivity and Majorana bound states in hybrid superconductor-semiconductor structures. Graph adapted from Phys. Rev. Lett. 118, 107701, https://doi.org/10.1103/PhysRevLett.118.107701

Key publications

• Minimal Entanglement Witness from Electrical Current Correlations F. Brange, O. Malkoc, and P. Samuelsson. Phys. Rev. Lett. 118, 036804 (2017). See article minimal entanglement witness at publisher's site
• Subdecoherence Time Generation and Detection of Orbital Entanglement in Quantum Dots F. Brange, O. Malkoc, and P. Samuelsson. Phys. Rev. Lett. 114, 176803 (2015). See article subdecoherence time generation at publisher's site
• Two-Dimensional Platform for Networks of Majorana Bound States, M. Hell, M. Leijnse, and K. Flensberg, Phys. Rev. Lett. 118, 107701 (2017).  See article Two-dimensional platform at the publisher's site
• Tsintzis, A. et al. Creating and detecting poor man's Majorana bound states in interacting quantum dots. Physical Review B. 106, 20, L201404

Contact persons:

• Stefan Kröll
• Martin Leijnse
• Ville Maisi
• Tönu Pullerits
• Stephanie Reimann
• Peter Samuelsson
• Claes Thelander  
• Andreas Wacker