This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Working in close collaboration, researchers from Paderborn University, the University of Basel and Ruhr University Bochum have made a breakthrough in quantum communication. In their recently published paper in the journal Physical Review Letters, they demonstrate how special semiconductor nanostructures can be used to generate individual photons and pairs of photons that are almost perfectly identical.
These "indistinguishable" particles form the basis for quantum entanglement and quantum interference. In quantum information processing, photons are ideal carriers of information. However, to use these light particles for complex calculations, they must possess exactly the same properties—an aspect known as "indistinguishability." Until now, such sources have suffered from the fact that the photons generated were temporally correlated or out of focus, which greatly reduced their indistinguishability and thus their quality.
A team of doctoral candidates from Basel and Paderborn has now solved this problem using a process known as "biexciton decay" in semiconductor quantum dots within an optical resonator. This is a process in which a molecule consisting of two bound excitons (each a pair comprising an electron and an electron hole) decays, leaving behind a single exciton and a photon. "The so-called 'biexciton cascade' in a semiconductor quantum dot emits photons at the push of a button, which are of great interest for modern applications.
This is a process in which a quantum dot is doubly excited and the excitation then decays. This generates two photons, one after the other," explains lead author Timon Baltisberger from the University of Basel. "A quantum dot is often described as an artificial atom within a semiconductor that can generate individual particles of light.
By integrating it into a specialized optical cavity—similar to that found in a laser—the light emission process was specifically accelerated and controlled in this study," explains Dr. Stefan Schumacher, head of the "Theory of Functional Photonic Structures" research group at the Department of Physics and the Institute for Photonic Quantum Systems (PhoQS) at Paderborn University. Over the past few years, Professor Richard Warburton's research group at the University of Basel has conducted intensive research into the interaction of these quantum dots with optical cavities and has made progress in various fields.
The researchers have now been able to apply this expertise to the biexciton to accelerate its decay in a controlled manner. This results in photons of much higher quality: they are 90% indistinguishable, whereas without this effect the figure is merely 60%—a striking improvement. "The results show excellent agreement with the theoretical prediction and point the way toward generating photons with even higher indistinguishability.
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