Physicists at Paderborn University have, for the first time, experimentally demonstrated the so-called ‘return’ of Rabi oscillations in semiconductor quantum dots. The phenomenon, which was first predicted theoretically back in 2007, describes the decrease in the emission intensity of the quantum dots, which are initially dampened by interactions with the lattice vibrations of a solid (phonons). Only through sufficiently strong optical excitation can the original intensity be restored and the oscillation ‘reawaken’: an effect that previously existed only in idealised theoretical models and has now been proven. The results, published in the prestigious journal *Physical Review Letters*, mark a decisive step towards scalable quantum applications.

“It is a milestone that we can now finally observe and understand this fundamental quantum mechanical effect experimentally,” says Prof. Dr Klaus Jöns, head of the “Hybrid Quantum Photonic Devices” research group in the Department of Physics. “Our results show that, using semiconductor quantum dots, we are now able to control quantum-optical processes with a precision that was previously only possible with natural atoms,” Prof. Jöns continues.

The team succeeded in demonstrating this thanks to their many years of experience with specialised GaAs quantum dot samples, which were developed in close collaboration with Prof. Dr Armando Rastelli from the Johannes Kepler University of Linz. The experimental data were analysed and verified in collaboration with the ‘Theory of Functional Photonic Structures’ research group led by Prof. Dr Stefan Schumacher, also from the Department of Physics at Paderborn University, and the research group led by Prof. Dr Doris Reiter at TU Dortmund. “Our theoretical models were not only able to explain the experimental findings, but also to refine them,” says Prof. Schumacher. “The reappearance of Rabi oscillations is not an isolated effect, but a clear indication of the high coherence and controllability of the quantum dots.” The physicists are also conducting research on and with quantum systems at the Institute for Photonic Quantum Systems (PhoQS) at Paderborn University, where their work includes the fields of quantum simulation, communication, metrology and computing.

“Controlling such quantum mechanical processes using semiconductor technology represents a leap forward for the development of quantum computers, quantum communication systems and novel photonic components,” emphasises Prof. Jöns. “We demonstrate that artificial atoms in semiconductors have now reached a level of quality that can stand up to comparison with natural atoms.”