Quantum physics: Record entanglement of quantum memories

Researchers from LMU and Saarland University have entangled  quantum recollections over a 33-kilometer-lengthy fiber optic connection — a report and an critical step closer to the quantum net.

A community wherein statistics transmission is flawlessly stable towards hacking? If physicists have their manner, this could sooner or later turn out to be a fact with the assist of the quantum mechanical phenomenon called entanglement. For entangled debris, the guideline of thumb is: If you degree the nation of one of the debris, you then definately routinely realize the nation of the other. It makes no distinction how a long way away the entangled debris are from every other. This is a super situation for transmitting facts over lengthy distances in a manner that renders eavesdropping impossible.

A crew led via way of means of physicists Prof. Harald Weinfurter from LMU and Prof. Christoph Becher from Saarland University have now coupled  atomic quantum recollections over a 33-kilometer-lengthy fiber optic connection. This is the longest distance to date that everyone has ever controlled entanglement through a telecom fiber. The quantum mechanical entanglement is mediated through photons emitted via way of means of the 2 quantum recollections. A decisive step become the researchers’ transferring of the wavelength of the emitted mild debris to a price this is used for traditional telecommunications.

Generally speaking, quantum networks encompass nodes of character quantum recollections — including atoms, ions, or defects in crystal lattices. These nodes are capable of receive, store, and transmit quantum states. Mediation among the nodes may be achieved the use of mild debris which can be exchanged both over the air or in a focused way through fiber optic connection. For their test, the researchers use a device made out of  optically trapped rubidium atoms in  laboratories at the LMU campus. The  places are linked through a 700-meter-lengthy fiber optic cable, which runs below Geschwister Scholl Square in the front of the primary constructing of the university. By including more fibers on coils, connections of as much as 33 kilometers in duration may be achieved.

A laser pulse excites the atoms, and then they spontaneously fall lower back into their floor nation, every thereby emitting a photon. These mild debris can then be used to create a quantum mechanical coupling of the 2 atoms. To do this, the scientists despatched them thru the fiber optic cable to a receiver station, in which a joint dimension of the photons suggests an entanglement of the quantum recollections.

However, maximum quantum recollections emit mild with wavelengths withinside the seen or near-infrared variety. For this reason, the physicist from Saarbrücken and his crew optimized the wavelength of the photons for his or her adventure withinside the cable. Using  quantum frequency converters, they elevated the unique wavelength from 780 nanometers to a wavelength of 1,517 nanometers. The telecom band is the frequency variety wherein the transmission of mild in fiber optics has the bottom losses. Becher’s crew achieved the conversion with an extraordinary performance of fifty seven percent. At the equal time, they controlled to hold the exceptional of the facts saved withinside the photons to a excessive degree, that’s a circumstance of quantum coupling.

“The importance of our test is that we genuinely entangle  desk bound debris — this is to say, atoms that feature as quantum recollections,” says Tim van Leent, lead writer of the paper. “The test is an critical step at the direction to the quantum net primarily based totally on present fiber optic infrastructure,” says Harald Weinfurter.

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