Now how

How have scientists managed to stop light?

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A team of researchers at the University of Darmstadt in Germany.

What?

According to Albert Einstein, light is the fastest thing in the universe, and at a speed of 300 million meters per second, this isn’t hard to believe. For well over a decade, though, people have been working to stop light in its tracks and hold it in place. This isn’t the same as blocking the pathway of light like holding a book in front of a flashlight so it can’t shine through; this is stopping light completely, holding it in place, and releasing it.

In 1999, researchers were able to slow down the speed of light to 17 meters per second. In 2001, another team was able to stop light altogether, but for just a fraction of a second. Earlier in 2013, that time was increased to 16 seconds, but now, a team of German researchers at the University of Darmstadt has increased that stopped time further to a record-breaking full minute (Yirka).

When considering light, one minute is an incredibly long time. In one minute, light travels 18 billion meters. To put this in perspective, 18 billion meters is more than 20 round trips to the moon! Being able to store something that has the capacity to travel 18 billion meters is certainly a major milestone to celebrate.

Why?

Stopping light isn’t just a party trick for scientists to show off like running across a pool of liquid made of cornstarch and water and saying that it’s magic, although I do admit that this is still pretty cool:

light1

Harnessing light’s incredible speed could be the key to both developing super-powerful quantum computers and connecting them to high-speed, high-capacity quantum networks. Quantum computers, like their name suggests, store data based on the quantum state of individual atoms. This works well when transporting data through circuitry within a single processor or motherboard, but fails outside of this environment because the quantum coherence of atoms is easily disrupted by external factors such as background noise due to its exceptionally small size.

In order to solve this issue, quantum computers call for a quantum network that will easily transmit quantum-encoded data between different processors. The best way scientists have considered doing so is by encoding the data within the electromagnetic field of a beam of light, using the quantum state of photons rather than atoms.

Unfortunately, this can’t work with uninterrupted light because light requires time to be switched, routed, gatewayed, and tunneled from one processor to another, the same way that any link between two computers needs to be worked. In order to make this transmission of data work, the light (or the photons in the light) carrying the data must be stopped and stored.

According to George Heinze, a researcher on the team at the University of Darmstadt, their success in stopping light is the first step in building a “quantum repeater” that can store light data and emit the photons later with their quantum states intact, which would in turn lead to breakthroughs in data transmission speeds (Fogarty).

How?

light3The German researchers captured the light inside a crystal using a technique called electromagnetically induced transparency (EIT). The crystal was a cryogenically cooled mass of yttrium silicate doped with praseodymium. A control laser is fired at the crystal, triggering a quantum-level reaction that turned the crystal transparent. While the control laser is still firing, a light source carrying the quantum-based data is beamed into the transparent crystal. The control laser is then turned off, returning the crystal to its original opaque state. The light is left trapped inside the crystal and the opacity means that it can no longer bounce around.

Since the light is completely immobilized, the energy of the photons is picked up by atoms within the crystal. The photons are converted into atomic spin excitations (spin waves), which can then be stored into the crystal’s atoms. To get the light back out of the crystal, the control laser is turned on, reinstating its transparency, and the data on the atoms is returned to the photons.

The data in this particular experiment was a simple image of 3 horizontal lines. The data was able to retain its coherence as spin waves in the crystal for one minute before it faded out. The scientists believe that the data could be stored for longer periods using other crystals and specifically tailored magnetic fields (Anthony).

 

So?

It’s hard to tell how long it will take before this becomes a viable method of transmitting large amount of data, but this breakthrough has incredible implications for the future of quantum computing and beyond. This discovery will further light-based research.  There is also the potential implication that if we can stop light and control its emission, we can perhaps gain clues about accelerating it beyond the universal speed limit of 300 million meters per second.

 Written by Constance Kaita

Works Referenced 

Images courtesy of theverge.com, hight3ch.com, thedailymail.co.uk

Anthony, Sebastian. “Light stopped completely for a minute inside a crystal: The basis of quantum memory.” ExtremeTech.com. 25 July 2013. Web. 29 July 2013.

Fogarty, Kevin. “Building Superfast Networks by Stoppin Light.” Slashdot.org. 26 July 2013. Web. 29 July 2013.

Yirka, Bob. “Researchers stop and store light for 60 seconds.” Phys.org. 26 July 2013. Web. 29 July 2013.

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