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University of Basel

13 June 2022

Twin photons from unequal sources

quantum dots and photons
Although the quantum dots of the Basel researchers are different, they emit exactly identical light particles. (Image: University of Basel, Department of Physics)

Identical light particles (photons) are important for many technologies that are based on quantum physics. A team of researchers from Basel and Bochum has now produced identical photons with different quantum dots – an important step towards applications such as tap-proof communications and the quantum internet.

Many technologies that make use of quantum effects are based on exactly equal photons. Producing such photons, however, is extremely difficult. Not only do they need to have precisely the same wavelength (colour), but their shape and polarization also have to match.

A team of researchers led by Richard Warburton at the University of Basel, in collaboration with colleagues at the University of Bochum, has now succeeded in creating identical photons originating from different and widely-separated sources.

Single photons from quantum dots

In their experiments, the physicists used so-called quantum dots, structures in semiconductors only a few nanometres in size. In the quantum dots, electrons are trapped such that they can only take on very specific energy levels. Light is emitted on making a transition from one level to another. With the help of a laser pulse that triggers such a transition, single photons can thus be created at the push of a button.

“In recent years, other researchers have already created identical photons with different quantum dots”, explains Liang Zhai, a postdoctoral researcher and first author of the study that was recently published in Nature Nanotechnology. “To do so, however, from a huge number of photons they had to pick and choose those that were most similar using optical filters.” In that way only very few usable photons remained.

Original publication

Liang Zhai, Giang N. Nguyen, Clemens Spinnler et al.
Quantum interference of identical photons from remote GaAs quantum dots.
Nature Nanotechnology (2022), doi: 10.1038/s41565-022-01131-2

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