Quantum Entanglement Between Matter And Light Sent Over 50 Km Of Optical Fiber

Last Updated on

Eddie Gonzales Jr. – MessageToEagle.com – “When shared between remote locations, entanglement opens up fundamentally new capabilities for science and technology. Envisioned quantum networks use light to distribute entanglement between their remote matter-based quantum nodes…” researchers write in their paper.

The quantum internet promises absolutely tap-proof communication and powerful distributed sensor networks for new science and technology. However, because quantum information cannot be copied, it is not possible to send this information over a classical network.

In a nonlinear crystal illuminated by a strong laser the photon wavelength is converted to the optimal value for long-distance travel. Credit: IQOQI Innsbruck/Harald RitschIn a nonlinear crystal illuminated by a strong laser the photon wavelength is converted to the optimal value for long-distance travel. Credit: IQOQI Innsbruck/Harald Ritsch

Quantum information must be transmitted by quantum particles, and special interfaces are required for this.

Researchers at the Department 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 entanglement between matter and light. For the first time, a distance of 50 kilometers was covered using fiber optic cables.

“This is two orders of magnitude further than was previously possible and is a practical distance to start building inter-city quantum networks,” Ben Lanyon, the Innsbruck-based experimental physicist who is investigating these important intersections of a future quantum Internet, said in a press release.

Lanyon’s team started the experiment with a calcium atom trapped in an ion trap. Using laser beams, the researchers write a quantum state onto the ion and simultaneously excite 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. But the challenge is to transmit the photon over fiber optic cables.

“The photon emitted by the calcium ion has a wavelength of 854 nanometers and is quickly absorbed by the optical fiber,” says Ben Lanyon.

His team therefore initially sends the light particle through a nonlinear crystal illuminated by a strong laser.

Thereby the photon wavelength is converted to the optimal value for long-distance travel: the current telecommunications standard wavelength of 1550 nanometers. The researchers from Innsbruck then send this photon through a 50-kilometer-long optical fiber line. Their measurements show that atom and light particle are still entangled even after the wavelength conversion and this long journey.

As a next step, researchers show that their methods would enable entanglement to be generated between ions 100 kilometers apart and more. Two nodes send each an entangled photon over a distance of 50 kilometers to an intersection where the light particles are measured in such a way that they lose their entanglement with the ions, which in turn would entangle them.

With 100-kilometer node spacing now a possibility, one could, therefore, envisage building the world’s first intercity light-matter quantum network in the coming years: only a handful of trapped ion-systems would be required on the way to establish a quantum internet between Innsbruck and Vienna, for example.

Paper

Written by Eddie Gonzales Jr. – MessageToEagle.com Staff