Entangled Light Stored in Cooled Atoms

Scientists succeed in conserving partial light entanglement

For the first time, researchers report to have succeeded in creating an entangled-light atomic memory by combining quantum entanglement with the ability of bringing light to a complete halt, inside an ultracold atomic cloud. The entangled light was captured, stored for a short amount of time, then released back into the environment without losing the quantum link in the process. The two storage points have been located at a distance of only one millimeter apart, thus enabling the demonstration of entanglement between two atomic clouds and quantum teleportation to transmit a quantum state between the two clouds.

Theoretically, ultracold atomic clouds could span into space as much as a thousand kilometers to enable quantum telecommunications and transmission of messages encoded with unbreakable encryption codes. In 2001, a Harvard University team led by physicist Lene Hau demonstrated for the first time that light could be stopped in its tracks. By pulsing a laser beam into a cooled atomic cloud, reaching temperatures close to -273,15 degree Celsius or absolute zero, they were able to considerably slow the speed of the beam of light, until it froze in the quantum state of the atoms, then it was released into the medium once again.

Now, California Institute of Technology physicist H. Jeff Kimble claims to have succeeded in controlling a beam of light within a cesium cloud of gas. First, the beam of light was passed through a beam splitter cleaving a single photon into an entangled state, after which the photon was introduced and collected into the cesium cloud cooled to 125 millionths of a Kelvin above absolute zero, with the two storage points only one millimeter away from each other. By doing so, the research team was able to conserve up to 20 percent of the original entanglement after the release of the photon back into the surrounding environment.

It might not look like a very efficient way to conserve entanglement, however it is a big step forward, improving entanglement storage devices. Kyung Soo Choi, author of the study and physics PhD candidate at Caltech, says: "If we can generate entanglement every time we push a button, we can scale entanglement".

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