Quantum information

An ability to utilize quantum resources like the superposition of states and entanglement opens completely new perspectives for technology. The research focus of both experiment and theory is on generating and controlling long-lived coherent states and entanglement in different systems on the nanoscale.

Project areas:

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 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 concerns non-linear entanglement witnesses and deterministic, on-demand generation of pairs of entangled electrons.

Superconducting proximity effect and topological quantum computation.

We theoretically investigate different ways of exploiting superconducting proximity effect in semiconductors for fundamental physics experiments and for applications related to quantum information processing. One activity is topological superconductivity and Majorana bound states in hybrid superconductor-semiconductor structures. 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 or in gate-controlled superconducting qubits.

Topological superconductivity and Majorana bound states in hybrid superconductor-semiconductor structures
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

Coupling Spin Qubits via Superconductors. Martin Leijnse and Karsten Flensberg. Phys. Rev. Lett. 111, 060501 (2013)
See article coupling spin qubits at publisher's site

Key faculty

Recent theses

Sara Kheradsoud, Thermoelectric Effects and Single Electron Sources in Mesoscopic Transport; a Scattering Approach. PhD Thesis, Lund University 2019.
See Sara Kheradsoud's thesis in the Research Portal

Fredrik Brange, Quantum Correlations and Temperature Fluctuations in Nanoscale Systems. PhD Thesis, Lund University 2019
See Fredrik Brange's thesis in the Research Portal

Adam Kinos, Light-Matter Interaction and Quantum Computing in Rare-Earth-Ion-Doped Crystals. PhD Thesis, Lund University 2018
See Adam Kinos' thesis in the Research Portal

Johannes Bjerlin, Few- to many-body physics in ultracold gases: An exact diagonalization approach. PhD Thesis, Lund University, 2017
See Johannes Bjerlin's thesis in the Research Portal