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Caption: A study in Denmark may have made a significant advancement towards constructing a complex quantum photonic circuit needed for a quantum network.

Researchers have developed the first building blocks needed to construct a complex quantum photonic circuits needed for quantum networks.

Scientists from the Niels Bohr Institute in Denmark recently presented a study that shows that advanced photonic nanostructures are well on their way to revolutionizing quantum technology for quantum networks based on light.

Peter Lodahl, professor and head of the Quantum Photonics research group at the Niels Bohr Institute, University of Copenhagen, explained the latest advancement.

"We have developed a photonic chip, which acts as a photon gun,” Lodahl said in a statement. “The photonic chip consists of an extremely small crystal that is 10 microns wide and is 160 nanometers thick.

“Embedded in the middle of the chip is a light source, which is a so-called quantum dot. Illuminating the quantum dot with laser light excites an electron, which can then jump from one orbit to another and thereby emit a single photon at a time. Photons are usually emitted in all directions but the photonic chip is designed so that all the photons are sent out through a photonic waveguide,” he added.

The research group developed and tested the photonic chip until it achieved extreme efficiency, which Lodahl said was surprising that they can get the photon emission to occur in a way that was not previously thought possible.

Photons are normally transmitted in both directions in the photonic waveguide but in their custom-made photonic chip they could break the symmetry and get the quantum dot to differentiate between emitting a photon right or left, that means emit directional photons.

"The photons can be sent over long distances via optical fibers, where they whiz through the fibers with very little loss,” Lodahl said. “You could potentially build a network where the photons connect small quantum systems, which are then linked together into a quantum network—a quantum internet.”

Quantum technology based on light or photons is called quantum photonics, while electronics is based on elections. A quantum entity is the smallest unit in the microscopic world.

Photons are the fundamental constituent of light and electrons of electric current.

Electrons can be isolated to conduct current one electron at a time, while photons prefer to bunch together.

However, it is necessary to emit and send one photon at time since information for quantum communication based on photonics is encoded in a single photon.

Photons interact only very weakly with the environment—unlike electrons—meaning photons do not lose much energy along the way and can be sent over long distances.

This gives information based on photons great advantages because they are very well suited for carrying and distributing information and a quantum network based on photons will be able to encode much more information than is possible with current computer technology and the information could not be intercepted en route.

For quantum networks to work the ability to create a stream of single photons on demand is needed.

Lodahl said the next step is to expand the functionalities to large, complex quantum networks.

The study was published in Nature.

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