The quantum Internet promises absolutely tap-proof communication and powerful distributed sensor networks for new science and technology. However, since quantum information can not be copied, it is not possible to send this information over a classic network. Quantum information must be transmitted by quantum particles, and special interfaces are required. The Innsbruck experimental physicist Ben Lanyon, who was awarded the Austrian START Prize for his research in 201
Now his team at the Institute of Experimental Physics at the University of Innsbruck and at the Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences has achieved a record for the transfer of quantum entanglements between matter and light. For the first time, 50 kilometers were covered with fiber optic cables. "This is two orders of magnitude more possible and a practical distance to begin building quantum networks between cities," says Ben Lanyon.
Converted Photon for Transmission
Lanyon's team started the experiment with a calcium atom trapped in an ion trap. Using laser beams, the researchers write a quantum state on the ion and simultaneously stimulate it to emit a photon in which quantum information is stored. As a result, the quantum states of the atom and the light particle are entangled. The challenge, however, is to transmit the photon via fiber optic cable. "The photon emitted by the calcium ion has a wavelength of 854 nanometers and is rapidly absorbed by the optical fiber," says Ben Lanyon. His team first sends the light particle through a non-linear crystal, which is illuminated by a strong laser. The photon wavelength is converted to the optimum value for long-distance travel: the current standard telecommunications wavelength of 1550 nanometers. The Innsbruck researchers then send this photon over a 50-kilometer-long fiber optic cable. Their measurements show that atomic and light particles are still entangled even after the wavelength conversion and this long journey.
Greater Distances in Sight
As a next step, Lanyon and his team show that their methods would allow entanglement between ions 100 kilometers apart and more. Two nodes each send an entangled photon over a distance of 50 kilometers to an intersection point at which the light particles are measured so that they lose their entanglement with the ions, which in turn would entangle them. With a node distance of 100 kilometers, one could therefore imagine building the world's first light matter intercity quantum network in the coming years: on the way to building a quantum internet between Innsbruck, only a handful of trapped ion systems would be required, and Vienna, for example ,
Lanyon's team is part of the Quantum Internet Alliance, an international project funded by the European Union's Quantum Flagship. The current results were published in the Nature Journal Quantum Information .
Researchers are developing practical methods for measuring quantum entanglement
V. Krutyanskiy et al., Entanglement of Light Matter over 50 km of Optical Fiber, npj Quantum Information (2019). DOI: 10.1038 / s41534-019-0186-3
Entanglement over 50 km of fiber optics sent (2019, 29th August)
retrieved on August 29, 2019
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