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Experimental mastery of complex quantum systems is needed for future technologies such as quantum computers and quantum encryption. Scientists from the University of Vienna and the Austrian Academy of Sciences have innovated. They have sought to use more complex quantum systems than entangled qubits in two dimensions and can thus increase the information capacity with the same number of particles. The methods and technologies developed could in the future allow the teleportation of complex quantum systems. The results of their work, "Greenberger-Horne-Zeilinger's Experimental Entanglement Beyond Qubits", are published recently in the well-known journal Photonic Nature.
Similar to the bits of classical computers, qubits are the smallest unit of information in quantum systems. Big companies like Google and IBM are competing with research institutes around the world to produce a growing number of entangled qubits and develop a functional quantum computer. But a research group from the University of Vienna and the Austrian Academy of Sciences is pursuing a new path to increase the information capacity of complex quantum systems.
The underlying idea is simple: instead of simply increasing the number of particles involved, the complexity of each system is increased. "The peculiarity of our experience is that, for the first time, it entangles three photons beyond conventional two-dimensional nature," says Manuel Erhard, first author of the study. To this end, Viennese physicists have used quantum systems with more than two possible states – in this particular case, the kinetic momentum of individual luminous particles. These individual photons now have a higher information capacity than qubits. However, the entanglement of these light particles has proven difficult conceptually. The researchers overcame this challenge with a groundbreaking idea: a computer algorithm that searches autonomously for an experimental implementation.
With the help of a computer algorithm called Melvin, the researchers found an experimental setup to produce this type of entanglement. At first, it was very complex, but it worked in principle. After some simplifications, physicists still faced major technological challenges. The team was able to solve these problems with advanced laser technology and a specially developed multi-port system. "This multi-port is the heart of our experience and combines the three photons to entangle them in three dimensions," explains Manuel Erhard.
The particular property of three-dimensional three-photon entanglement allows an experimental investigation of new fundamental questions about the behavior of quantum systems. In addition, the results of this work could also have a significant impact on future technologies, such as quantum teleportation. "I think the methods and technologies we have developed in this publication allow us to teleport a larger proportion of the total quantum information of a photon, which could be important for quantum communication networks" , says Anton Zeilinger.
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More information:
Manuel Erhard et al, Experimental Greenberger – Horne – Zeilinger, entanglement beyond qubits, Photonic Nature (2018). DOI: 10.1038 / s41566-018-0257-6
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