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Quantum Internet is one step closer to reality with US research breakthrough


  Non-Linear Crystal

US-funded University of Innsbruck researchers achieved a record for transferring quantum entanglement between matter and light – 50 kilometers covered of optical cables. According to researchers, this brings the quantum internet closer. In a nonlinear crystal illuminated by a strong laser, the photon wavelength is converted to the optimum value for long-distance travel. Credit: IQOQI Innsbruck / Harald Ritsch

Triangle Park Research, New York – US Army research findings are pushing quantum internet closer. Such an Internet could offer military security, intelligence and time-keeping capabilities that are not possible with traditional networking approaches.

US Army Quantitative Information Center for Dissemination Information, funded and operated by the Army's Office of Laboratory Research, saw researchers at the University of Innsbruck achieve a record for the transfer of quantum entanglement between matter – distance of 50 kilometers by means of optical cables.

Interlacing is a correlation that can be created between quantum entities such as cubes. When two cubes are tangled and one of them is measured, it will affect the result of the measurement made by the other, even if the latter is physically far away.

"This [50 kilometers] is two orders of magnitude larger than previously possible, and it's a practical distance to start building long-distance quantum networks," says Dr. Ben Lyon, an experimental physicist at the University of Innsbruck and a principal investigator on the project. , whose findings were published in the journal Nature Quantum Information (see citation below)

Long-distance quantum networks will consist of remote network nodes of physical cubes, which, despite their large physical separation, are still entangled. This distribution of entanglement is essential to creating a quantum Internet, researchers said.

"The demonstration is a major step forward in achieving a large-scale entanglement distribution," says Dr. Sarah Gamble, co-director of the Army Research Support Program, "The quality of braiding after fiber travel is also high enough at the other end, to meet some of the requirements for some of the toughest quantum network applications. "

The research team began an experiment with a calcium atom trapped in an ion trap. Using laser beams, the researchers wrote a quantum state on the ion and simultaneously excited it to emit a photon in which quantum information was stored. As a result, the quantum states of the atom and the light particle were entangled.

The challenge is to transfer the photon over optical cables.

"The photon emitted by the calcium ion has a wavelength of 854 nanometers and

his team initially sends the light particle through a non-linear crystal illuminated by a strong laser. The photon wavelength was converted to the optimum value for long-distance travel – the current telecommunications standard wavelength of 1550 nanometers.

The researchers then sent this photon through a 50-kilometer optical fiber line. Their measurements show that the atomic and light particles were still entangled even after the transformation of the wavelength and the distance traveled.

"The choice to use calcium means that these results also provide a direct path to realizing a tangled web of atomic clocks over a great physical distance, since calcium can be captured by a high-quality quartile clock. Large-scale intricate clock networks are of great interest to the Army for position accuracy, navigation, and synchronization applications, "said Dr. Fredrick Fatemi, an Army researcher who also directs the program.


The CCDC Army Research Laboratory (ARL) is an element of the command of the United States Army's combat capability development. As an Army Corporate Research Laboratory, ARL discovers innovations and the transition of science and technology to secure dominant strategic land power. Through collaboration in the core technical competencies of the command, CCDC is leading the discovery, development, and provision of technology-based capabilities necessary to make soldiers more effective in winning our nation's wars and returning home safely. CCDC is the principal subordinate command of the US Army Futures Command.

Reference: "Light matter entanglement over 50 km optical fiber" by V. Krutyanski, M. Meraner, J. Schup, V. Krmakarski, H. Heinzer and BP Lanyon, 27 August 2019, npj Quantum information .
doi: 10.1038 / s41534-019-0186-3

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