Pushing the envelope of Albert Einstein's "spooky action at a distance," known as entanglement, researchers at the Joint Quantum Institute (JQI) of the Commerce Department's National Institute of Standards and Technology and the University of Maryland have demonstrated a "quantum buffer," a technique that could be used to control the data flow inside a quantum computer. Quantum computers could potentially speed up or expand present capabilities in decrypting data, searching large databases, and other tasks. The new research is published in the Feb. 12 issue of the journal Nature.
"If you want to set up some sort of communications system or a quantum information-processing system, you need to control the arrival time of one data stream relative to other data streams coming in," says JQI's Alberto Marino, lead author of the paper. "We can accomplish the delay in a compact setup, and we can rapidly change the delay if we want, something that would not be possible with usual laboratory apparatus such as beamsplitters and mirrors," he says.
This new work follows up on the researchers' landmark creation in 2008 of pairs of multi-pixel quantum images (http://www.physorg.com/news132500362.html). A pair of quantum images is "entangled," which means that their properties are linked in such a way that they exist as a unit rather than individually. In the JQI work, each quantum image is carried by a light beam and consists of up to 100 "pixels." A pixel in one quantum image displays random and unpredictable changes say, in intensity, yet the corresponding pixel in the other image exhibits identical intensity fluctuations at the same time, and these fluctuations are independent from fluctuations in other pixels. This entanglement can persist even if the two images are physically disconnected from one another.
By using a gas cell to slow down one of the light beams to 500 times slower than the speed of light, the group has demonstrated that they could delay the arrival time of one of the entangled images at a detector by up to 27 nanoseconds. The correlations between the two entangled images still occur—but they are out of sync. A flicker in the first image would have a corresponding flicker in the slowed-down image up to 27 nanoseconds later.
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