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Qubit Mechanical Resonator

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 Entanglement Image

Researchers reveal the first ever image of quantum entanglement

Scientists for the first time have managed to capture the first actual photo of quantum entanglement in the world. This phenomenon was so strange that Albert Einstein described it as a spooky action at a distance. This study has been published in the journal Science Advances.

This breathtaking image was captured by the scientists at the University of Glasgow in Scotland. From an aesthetic point of view, it may not look much however if it is looked at this way that this grey image is the first time we have observed the particle interaction that forms the cornerstone of quantum computing and underpins the odd science of quantum mechanics, then it is indeed very special.

Quantum entanglement takes place when two particles are so closely linked that they cannot be separated and whatever happens to one of the particles affects the other one spontaneously, irrespective of the distance between them. Thus it was described as “a spooky action at a distance“. 

This image shows entanglement between two photons. They interacted for a short period of time sharing the physical states. Paul-Antoine Moreau, the first author of this paper said that the image demonstrated a very fundamental property of nature. For capturing the photo, the team of researchers made a system which blasted streams of photons entangled with each other at non-conventional objects. Then they split up the entangled photons and passed one of the beams through a liquid crystal object called β-Barium Borate, that triggered four phase transitions. They also took the photos of the entangled pair of photons simultaneously which were going through the phase transitions, although they did not pass through the liquid crystal. The camera managed to capture the images which showed that they shifted in the same direction even though they had already split up. Thus, in other words, they were entangled. 

Although Albert Einstein made quantum entanglement very famous all around the globe, it was another physicist named John Stewart Bell who actually defined quantum entanglement and also established a test known as “Bell Inequality”. True quantum entanglement can be confirmed if it is possible to break the Bell Inequality. 

The team mentioned in their report that in their experiment they were able to demonstrate the violation of Bell Inequality in the captured images. Thus one hand it opens up to new schemes of quantum imaging and it also promises possibilities of quantum information schemes based on spatial variables. 

Graphene

Researchers demonstrate working of quantum computers with help of graphene

A new material consisting of only one sheet of carbon atoms can give rise to new and unique designs of optical quantum computing devices. Researchers from the University of Vienna and Institute of Photonic Sciences, Barcelona have proved that tailored structures of graphene lead to the interaction of singular photons. The study has been published in the npj Quantum Information.

Photons interact with the environment to a very less degree, which makes it quite suitable for the storage and transmission of quantum information. However this same property makes it very difficult to interpret the information which has been stored in them.

For building a quantum photonic computer, it is essential for a photon to alter the state of second. This is called a quantum logic gate and a quantum computer requires millions of these. This can be achieved with the help of a ‘non-linear material’, in which there is interaction of two photons. But the standard non-linear materials are not efficient to construct a quantum logic gate.

However it has been recently understood that the nonlinear interactions can be highly improved with the help of plasmons. Plasmons make the light bind to the electrons which are located at the surface. Then these electrons facilitate a very strong interaction between the photons. In presence of these positives, a drawback is that the plasmons decay in the standard materials before the actual quantum effects can occur.

Philip Walther, from University of Vienna who led the team of researchers made a proposal to manufacture plasmons in the graphene material. Graphene has been only discovered in 2004 by Andre Geim and Konstantin Novoselov at University of Manchester. Though it was observed way back in 1962, it had not been independently isolated and studied then. For their work, the duo was awarded the Nobel Prize in Physics in 2010.

The unique arrangement of electrons in graphene leads to strong nonlinear interactions, which allows the plasmons to remain for a long duration. In the graphene quantum logic gate, scientists have demonstrated that if singular plasmons in nanoribbon are made from graphene, then it allows for the interaction of electrical fields of two plasmons in different nanoribbons. This makes way for quantum computation if each of the plasmons remain in their ribbons, since many gates can be applied to them.

Irati Alonso Calafell, who is the first author on this paper remarked that strong non linear interaction in graphene does not allow two plasmons to be in the same ribbon.