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English Logo - Department of Physics - TU Dortmund
Physikgebäude (Neubau Otto-Hahn-Str. 4a) an der TU Dortmund © Nikolas Golsch​/​TU Dortmund
PUBLICATION IN PHYSICAL REVIEW LETTERS

Question of interaction between spins in semiconductor quantum dot ensembles solved

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© WG Anders​​/​​TU Dortmund
The graphic shows quantum dots on a surface whose spins - excited by laser pulses (red and blue arrows) - interact with each other (black line).
The fact that spins in ensembles of semiconductor quantum dots, which are being discussed as candidates for quantum bits - so-called qubits - in quantum computers, interact with each other has been known for some time and experimentally proven. However, until now it was unclear which mechanism was behind it. This mystery has now been solved by a team from Theoretical Solid State Physics led by Prof. Frithjof Anders from the Faculty of Physics at TU Dortmund University. The scientists recently published their findings in the renowned journal Physical Review Letters.

Quantum dot ensembles can be simplified as a two-dimensional surface on which dots of different sizes are distributed at irregular intervals. One electron spin - the intrinsic angular momentum of electrons - is localized in each of these dots. The distances between them are so large that actually no interaction between the individual spins should take place. Experiments with laser pulses, however, have shown that the spins react to lasers with different frequencies, so there is indeed an interaction. "The research group of Prof. Manfred Bayer from the Faculty of Physics was already able to demonstrate experimentally in 2011 that the spins do interact with each other. For possible applications, however, it is essential to also understand the mechanism behind the interaction," says Prof. Frithjof Anders.

Results successfully reproduced

The team therefore created a theoretical model, constrained it using realistic basic assumptions and chose the parameters in such a way that the experimental results could be reproduced. "We were ultimately able to establish very good agreement between the experimental and theoretical results," reports Frederik Vonhoff. With the help of the model, it is now possible to predict how the interactions can be specifically influenced and adapted for certain applications. The findings could help improve the integration of quantum information processing hardware into standard computer hardware in the future.

The research was conducted as part of Collaborative Research Center/Transregio 160, "Coherent Manipulation of Interacting Spin Excitations in Tailored Semiconductors." From the team of Prof. Frithjof Anders, Frederik Vonhoff and Andreas Fischer as well as Kira Deltenre were significantly involved in the publication, which was recently published in the renowned journal Physical Review Letters.

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