Physicists stop and store light traveling in an optical fiber

May 11, 2015
Light propagating in a glass fiber can be halted and reemitted later on demand via its interaction with cold cesium atoms in the vicinity of an elongated area. This device provides an all-fibered memory for light, an essential ingredient for the creation of future quantum networks. Credit: Julia Fraud – Kastler Brossel

Researchers at the Kastler Brossel Laboratory in Paris have managed to store light that propagates in an optical fiber and to release it later on demand. By causing interaction between the traveling light and a few thousand atoms in the vicinity, they demonstrated an all-fibered memory.

In the May 8th issue of the Physical Review Letters, Prof. Julien Laurat and his colleagues at Pierre and Marie Curie University report that they have devised optical memory integrated into an . The team created a way to stop and store the that usually propagates in a fiber at a speed as fast as 200,000 kilometers per second. This capability represents an important advance in , as fibers are at the heart of our worldwide telecommunication system, but also for a future quantum Internet, in which quantum information can be transported and synchronized between interconnected nodes.

"This work provides a demonstration of an all-fibered memory for light. We have been able to store the light and release it later into the fiber," says Baptiste Gouraud, a graduate student who designed this experiment and the lead author of the paper. "Previous demonstrations were based on free-space ensembles of atoms, not on a wave-guided implementation compatible with fibers used in networks."

At the core of the device is a commercial fiber with a short section elongated to 400 nanometers in in diameter where the light can efficiently interact with a cloud of laser-cooled atoms. Using the so-called electromagnetically induced transparency technique, which is well-known in free space but combined here for the first time with a fiber, the researchers slowed down the light pulse by 3000-fold and then halted it completely. The information conveyed by the laser light is transferred to the atoms in the form of a collective excitation, a large quantum superposition. Around 2000 cesium very close to the fiber were involved in the process. Later, after a programmable period, the light was released into the fiber, reconstituting the initial encoded information that can once again travel. Storage times of up to 5 microseconds were demonstrated, corresponding to a traveling distance of 1 km if the light had not been halted.

The experiment by the Paris team also showed that even light pulses containing only one photon can be stored, with a very large signal-to-noise ratio. This feature will enable the use of this device as a quantum memory, an essential ingredient for the creation of future quantum networks.

Explore further: Glass fiber that brings light to standstill

More information: "Demonstration of a memory for tightly guided light in an optical nanofiber," Physical Review Letters 114, 180503 (2015). DOI: 10.1103/physrevlett.114.180503

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2.3 / 5 (3) May 11, 2015
This is impressive, but implies additional power supplies and time-keeping signals and other control signals, which still more than doubles complexity of the system, and implies you have another line of attack for hackers.
May 11, 2015
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not rated yet May 11, 2015
Sounds hideously expensive.
not rated yet May 12, 2015
Anyway we have to kept in mind that light pulses is an electromagnetic wave packet which have to propagates with constant speed c – no more or less; so here we must not interpret that light pulses really slow down or stop …..

Light only propagates with speed c in empty space. The article says
usually propagates in a fibre at a speed as fast as 200,000 kilometres per second
which is 2c/3 so stopping it is still impressive. As I understand it, the information is stored and then reconstituted.
not rated yet May 12, 2015
Light only propagates with speed c in empty space. The article says

usually propagates in a fibre at a speed as fast as 200,000 kilometres per second

which is 2c/3 so stopping it is still impressive.

A fiber is not empty space. 200k km/sec is the speed of light in an optical fiber.
The speed of light is (sometimes considerably) lower in a medium. This can be as low as walking speed.

What they did here is store it in the medium and recall it at will. The really cool part is that they did not have to involve another medium. Such an all-fiber memory means you can build the pathways and memory of a photonic (or quantum) computer from one and the same material (which is crucial for miniaturization and quality).

not rated yet May 12, 2015

A fiber is not empty space. 200k km/sec is the speed of light in an optical fiber.

That was my point. Sorry if I didn't express it clearly enough.
not rated yet May 18, 2015
It annoys the heck out me that popular science writers so misuse these words.

You can never change the speed of light. Never.

It doesn't travel more slowly through water; instead it has a longer free path because it doesn't travel in a straight line. Instead it "bounces around" yielding a longer path and creating the illusion it is travelling more slowly. It is also repeatedly absorbed and readmitted and that takes time. Againg it creates the illusion that the light has slowed.

Consider this: the space between any two molecules of H2O IS a vacuum. Alternatively one can argue "there are no such things as vacuums" which is true since all of space has a non-zero density.

You have to qualify statements like this with phrases like "on average" or in a volume of such pressure and temperature that we can consider it a vacuum or at least a near-vacuum.

But light does NOT travel slower in any medium of any material medium.

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