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Researchers successful in developing quantum light sources for use in optical circuits

A team of researchers led by Alexander Holleitner, Jonathan Finley, physicists at Technical University of Munich (TUM) has succeeded in placing light sources in atomically thin material layers having an accuracy of few nanometres. It allows a series of applications in quantum technology ranging from quantum sensors, transistors to encryption technology for transmission of data. The study has been published in Nature Communications

Earlier circuits on chips relied on electrons as carriers of information. However, in the coming days, photons carrying information at the speed of light will perform this task in optical circuits. The basic building blocks for such chips are quantum light sources connected with detectors and quantum fibre optic cables. 

Julian Klein, the study’s lead author said that it is a first step in making optical quantum computers. The light sources need to coupled with photon circuits for future applications to make quantum calculations based on light possible. However, the critical point is the exact controlled placement of the light sources. Quantum light sources in materials such as diamond or silicon can be created but not precisely placed in the materials. 

Physicists used a semiconductor layer, molybdenum disulfide as the initial material with a thickness of three atoms. Then they irradiated it with a beam of helium ions focused on a surface area of less than one nanometre. For generating optically active defects, molybdenum or sulfur atoms are hammered out of layer very precisely. The imperfections are traps for electron-hole pairs which emit the desired photons. The helium ion microscope at Center for Nanotechnology and Nanomaterials, Walter Schottky Institute was used for irradiating the material with accurate lateral resolution. 

Researchers from TUM, University of Bremen, Max Planck Society developed the model for describing the energy state observed at theoretical imperfections.

In future scientists want to create complex light source patterns, in two-dimensional lateral lattice structures for researching multi-exciton phenomena. This is the experimental realisation of the theory within the context of the Bose-Hubbard model, accounting for complex processes in solids. 

As the light sources have a similar underlying defect in the material they cannot be distinguished theoretically. This opens for new opportunities which are based on the quantum-mechanical principle of entanglement. Klein said that it is very much possible for the integration of quantum light sources in the photon circuits in a very elegant manner. Because of the high sensitivity, it is possible to make quantum sensors for smartphones and also make highly secure encryption technologies to transmit data. 

Journal Reference: Nature Communications

Quantum Dots with emission maxima in a 10-nm step are being produced at PlasmaChem in a kg scale

Researchers achieved near-perfect performance in low-cost semiconductors

Nowadays the whole world has become digitalized and for each and everything we have an electronic device. We have a television to entertain ourselves, an iPad to watch movies and work on the go, a mobile to receive calls when we are away from home. These electronic devices have something called as the semiconductor.

A semiconductor is a substance whose electrical conductance falls between metal and insulator. However, the conducting property can be altered by adding impurities into the crystal. Some commonly known semiconductors are silicon, germanium, and arsenide. Since it becomes very difficult to produce, semiconductor becomes very expensive.

Quantum dot is the solution and can be used in place of a semiconductor. Quantum dots are basically very small semiconductors which lie in the nanometre scale. Quantum dots change its properties even with a very small change in shape or size. The quantum dots have been used in electronic instruments like solar panels, camera sensors and medical imaging tools by researchers.

David Hanifi co-author of research on quantum dots said, “These quantum dots can be made in large number in labs in a more simple way as compared to semiconductor”.

When the research started in order to understand whether they could compete with semiconductors, the researchers focused on how efficiently the quantum dots could remit the light that they absorb, and the experiments showed that the performance of quantum dots was better as compared to a semiconductor.

This research work is the result of a collaboration between the labs of Alberto Salleo, professor of materials science and engineering at Stanford, and Paul Alivisatos, the Samsung Distinguished Professor of Nanoscience and Nanotechnology at the University of California, Berkeley, who is a pioneer in quantum dot research and senior author of the paper. However, this research is a part of the collection of projects of the Department of Energy at the Frontier Research Centre.

There are various benefits that quantum dots have. Being highly customizable, one of the biggest benefits of quantum dots is that it changes its shape due to which it can change the wavelength of light that they emit which is one of the biggest advantages in colour based applications like television.

Thus, quantum dots have hit the consumer market in the form of quantum dot TV or the QLED(where Q stands for quantum dots).

Samsung QLED TV

Samsung QLED TV 8K – 75 inches. Credit: Bretwa/ wikimedia

As we all know that everything in this universe comes with its own disadvantages, the disadvantage that the quantum dot has is that because of its smaller size – it takes many particles to come together in order to perform a particular task. In order to form so many quantum dots, the chances of something going wrong becomes highly possible, which indirectly means that the chances of some program to go wrong also becomes possible due to which there are chances of performance getting hampered.

The researchers are finding out measurement techniques in order to evaluate these particles.

The next step in the ongoing research involves even more precise measurements and if the researchers can determine that, these quantum dots could reach an efficiency of 99.9 percent or above.

With the increase in efficiency, we can have wonderful applications like:

  • New glowing dyes to enhance our ability to look at biology at the atomic scale.
  • Luminescent cooling and luminescent solar concentrators, which allow a relatively small set of solar cells to take in energy from a large area of solar radiation and many more things.

People working on these quantum dot materials have thought for more than a decade that dots could be as efficient as single crystal materials,” said Hanifi.

So, Let us hope for this research to go forward and get us many other efficient applications.

Published Researchhttp://science.sciencemag.org/content/363/6432/1199