Transport physics

Quantum dots in nanowires

We explore the physics of strongly confined quantum dots in semiconductor nanowires, formed by heterostructures and/or local gate potentials. Quantum dots behave as artificial atoms but with properties that can be changed during the experiments using electric and magnetic fields. Our primary focus is on understanding and controlling spin and orbital states in quantum dots and coupled quantum dots, which are key building blocks in many concepts for quantum information processing. We focus on nanowires because they already provide much of the required confinement and offer built-in contacts for transport measurements. Additionally, many interesting materials and heterostructures can only be synthesized in nanowires.

SEM image of an InAs nanowire with GaSb shell grown preferentially on zinc blende InAs (left). SEM image of quantum device showing position of gate electrodes and source-drain contacts to individually control each dot (right). Adapted from D. Barker et al, Appl. Phys. Lett. 114, 183502 (2019); https://doi.org/10.1063/1.5089275

Simulation schemes for quantum transport

We develop numerical tools for a quantitative simulation for electrical transport in nano-devices. Here we use a variety of different approaches ranging from the Pauli master equation, over different types of quantum master equations to Green's function approaches. In this context we established the open source code QMEQ which allows to compare different schemes. Our simulations are targeted to specific experimental designs and allow both to understand the underlying physics and to optimize electro-optical devices.

Key publications:

• Individually addressable double quantum dots formed with nanowire polytypes and identified by epitaxial markers. D. Barker, S. Lehmann, L. Namazi, M. Nilsson, C. Thelander, K. A. Dick, and V. F. Maisi. Appl. Phys. Lett. 114, 183502 (2019). See article individually addressable double quantum dots at publisher's site
• Kinetic equations for transport through single-molecule transistors. M. Leijnse, M. R. Wegewijs, Physical Review B 78, 235424 (2008). See article kinetic equations at publisher's site
• QmeQ 1.0: An open-source Python package for calculations of transport through quantum dot devices G. Kiršanskas, J. Nyvold Pedersen, O. Karlström, M. Leijnse, A. Wacker, Computer Physics Communications 221, 317 (2017). See article open-source Python package at publisher's site
• Electronic structure of quantum dots. S. M. Reimann and M. Manninen, Rev. Mod. Phys. 74, 1283, (2002). See article electronic structure of quantum dots at publisher's site
• Parallel-Coupled Quantum Dots in InAs Nanowires. M. Nilsson, I.-J. Chen, S. Lehmann, V. Maulerova, K. A. Dick, C. Thelander, Nano Letters 17, 7847 (2017). See article parallel-coupled quantum dots at publisher's site
• Tuning the two-electron hybridization and spin states in parallel-coupled InAs quantum dots. M. Nilsson, F. Viñas Boström, S. Lehmann, K. A. Dick, M. Leijnse, C. Thelander, Phys. Rev. Lett. 121, 156802 (2018). See article tuning the two-electron hybridization and spin states at publisher's site
• Potts. H, et al. Electrical control of spins and giant g-factors in ring-like coupled quantum dots, Nature Communications volume 10, Article number: 5740 (2019)

Contact persons:

• Adam Burke
• Heiner Linke
• Martin Leijnse
• Ville Maisi
• Stephanie Reimann
• Peter Samuelsson
• Claes Thelander
• Andreas Wacker