Temporal Control Of Light Echoes

Scientists succeed for the first time in targeted control of the common light emission from many nanosystems - publication in "Communications Physics"

Scientists from the University of Paderborn, the Technical University of Dortmund and the University of Würzburg have succeeded for the first time in using laser pulses to specifically control the so-called photon echo, which can arise when light waves are superimposed. The research results have now been published in the journal "Communications Physics" by the Nature Publishing Group.

“'How you shout into the forest, it echoes out' is not only a well-known expression, it is also literally true. If the sound wave is reflected, the echo sounds. When it comes back, however, depends on the forest - but above all on the distance between the caller and the place of reflection ”, explains Prof. Dr. Torsten Meier from the University of Paderborn. “Imagine if you could change the point in time at which the echo comes back to you as you like,” the physicist continues. A team of scientists has now achieved something like this. However, not for acoustic signals, but for optical signals: they have specifically controlled photon echoes that are emitted by semiconductor quantum dots below the second limit.

Meier explains: “Optical echoes are to be understood somewhat differently than conventional acoustic echoes, because they are not caused by the reflection of waves, but rather by a non-linear optical process. For this purpose, two short laser pulses are sent to a sample. The first corresponds to the signal and the second to the forest. So he takes care of the reflection. With twice the delay time of these pulses, the illuminated system emits a new light pulse, the photon echo. ”With another control pulse, the researchers were now able to control this photon echo in the range of picoseconds (this corresponds to 10 -12Seconds) and thus move it to a desired position in time. Such a control is particularly relevant for nanophotonic circuits in which many optical systems have to be precisely synchronized with one another.

The theoretical prediction of the effect is in the group of Prof. Dr. Torsten Meier emerged. The experimental implementation, which was carried out in the working group of Prof. Dr. Ilya Akimov (TU Dortmund): "The temporal control of optical echoes is a very robust effect in which the system is effectively stopped by the control pulse," says Hendrik Rose, doctoral student in Paderborn. Alexander Kosarev, PhD student at TU Dortmund University, adds: "This effect was recently theoretically predicted, could be implemented experimentally by us and offers a wide range of options for manipulating the light emission of semiconductor systems". The samples used were examined in the working group of Prof. Dr. Sven Höfling (University of Würzburg).

The research results came about as part of a collaboration funded by the German Research Foundation (DFG) through the Transregio 142 “Tailored Nonlinear Photonics”. Based on this first demonstration, the scientists now want to optimize the effect, for example by increasing the time shifts. In the future, the phenomenon is to be further developed in particular for novel applications in the field of photonic quantum technologies, which are being intensively researched at the Paderborn Institute for Photonic Quantum Systems (PhoQS).