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Saturday, November 26, 2022

Scientists create uniform photons from widely scattered sources

Uniform light particles (photons) are important for many quantum-physics-based technologies. Identical photons containing individual quantum dots have now been generated by a team of researchers from Basel and Bochum, paving the way for applications such as tap-proof communications and the quantum Internet.

Scientists Produce Similar Photons From Widely Scattered Sources.
Although the Basel researchers’ quantum dots are different, they emit exactly the same light particles. Image credits: University of Basel, Department of Physics.

Most quantum-based devices rely on photons which are all the same. However, making such photons is incredibly challenging. Not only must they have the same wavelength (colour), but they must also be of the same form and polarity.

In partnership with colleagues at Bochum University, a team of researchers led by Richard Warburton at the University of Basel has successfully produced identical photons obtained from different and widely dispersed sources.

Single photons from quantum dots

The researchers used quantum dots in their tests, which are tiny structures in semiconductors that are only a few nanometers in size. Electrons are confined in quantum dots, allowing them to occupy only very specific energy levels.

Light is emitted when moving from one level to another. Single photons can be created at the touch of a button using a laser pulse that induces such a transition.

In recent years, other researchers have already created similar photons with different quantum dots. However, to do this, they had to pick and choose from a large number of photons the ones that were most similar using optical filters.

Lian Zhai, Study first author and postdoctoral researcher, University of Baselu

As a result, only a few useful photons remained.

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Nature Nanotechnology study published.

A new, more ambitious method was employed by Warburton and his colleagues. To start, the Bochum scientists created ultrapure gallium arsenide, which was used to make quantum dots. As a result, the inherent difference between quantum dots can be kept to a minimum.

The electrodes were then used by the Basel researchers to expose the two quantum dots to finely adjusted electric fields. These fields changed the energy levels of the quantum dots, and they were adjusted so that all the photons released by the quantum dots had the same wavelength.

93 percent similar

The researchers used a half-silver mirror to show that the photons were virtually indistinguishable. He observed that light particles almost always traveled through mirrors as a pair or were reflected as a pair.

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They can conclude that the photons were 93% identical based on this finding. In other words, even though the photons were “born” completely independently of each other, they created twins.

In addition, the researchers were able to realize a key component of a quantum computer; Not Controlled Gate (or CNOT Gate). Quantum algorithms that handle specific problems significantly faster than conventional computers can be implemented using such gates.

Right now, our yield of identical photons is still around one percent. We already have a good idea, though, of how to increase that yield in the future.

Jiang Nguyen, PhD student, University of Basel

He was engaged in the execution of the experiment with his colleague Clemens Spindler. If the yield is increased, the twin-photon approach will be applicable in various quantum technologies.

identical photons from different sources

Same photons from different sources. Video credits: Swiss Nanoscience Institute and Department of Physics.

Journal Reference:

zhai l, and others, (2022) Quantum interference of identical photons from distant GaAs quantum dots. Nature Nanotechnology. doi:10.1038/s41565-022-01131-2.

Source: https://www.unibas.ch/en.html

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