Scientists "freeze" light inside a crystal for one minute


August 13, 2013

Scientists have managed to stop light within a crystal for up to one minute (Photo: TU Darmstadt)

Scientists have managed to stop light within a crystal for up to one minute (Photo: TU Darmstadt)

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Researchers at the Technische Universität Darmstadt in Germany have managed to stop light for up to one minute inside a crystal and store digitally-encoded information inside it. The technique shatters previous records and could prove very useful in developing faster and highly-efficient quantum and optical computers.

The switch to photonics

Today's technologies use semiconductor-based processors and storage devices to compute and store data electronically. However, with data being increasingly transmitted in the optical regime (e.g. through fiber optics), switching to all-optical components is appearing more and more like an appealing prospect.

Photons are much harder to interact with and manipulate than electrons, but if this hurdle can be cleared, switching from electronics to a photonics ecosystem would bring about many key advantages.

Electronic components dissipate a large portion of energy as heat, whereas in photonics components losses are very limited. Optical storage and computation would also be resistant to radiation, have a much higher transmission bandwidth, and allow for the manipulation of a single photon at a time, which would translate into better performance at a tiny fraction of the energy cost.

"Although classical data storage already offers very high read/write rates, optical data storage has the potential to be much faster," Georg Heinze, who was part of the research team, told Gizmag. "If everything operates in the optical regime there is no need to convert optical pulses in electronic signals and vice versa."

Bringing light to a halt

The information is retained in the crystal for up to one minute (Image: TU Darmstadt)

To store data in a photonics device, the researchers use a technique known as electromagnetically induced transparency (EIT).

EIT consists of firing a laser "control beam" at a crystal which contains ions of the element praseodymium. The laser triggers a quantum reaction in the crystal that has two contemporary effects. First, it makes this normally opaque crystal transparent over a narrow spectrum; and secondly, it changes the refractive index of the crystal dramatically, slowing the incoming light pulse down to a complete halt.

At this point, the researchers fire a second laser beam (containing the information to be stored) at the crystal. At the precise moment in which the laser beam carrying the information is crossing the temporarily transparent crystal, the control beam is turned off, trapping light and information inside the now opaque crystal. The photons are converted into atomic spin excitations (or "spin waves"), which can be stored in the crystal until the control beam is fired again and the spin waves are turned back into light, which finally escapes the crystal.

Scientists have used this technique in previous experiments, but they could only use it to store data for a few millionths of a second. This is because the spin wave is very delicate, subject to energy fluctuations that can corrupt the information it encodes.

The TU Darmstadt team figured out how they could prolong this storage time significantly. Their approach was to develop an algorithm that senses the noise and applies magnetic fields and high-frequency pulses to the crystal to maintain the spin wave in its original state, so that the information is kept safe for as long as possible – up to a minute.

"In this first proof-of-principle experiment we focused on long storage times rather than on transfer rates," says Heinze. "However, we showed that by image storage it is possible to increase the storage capacity of the memory, and this is very important feature for spatially multiplexed quantum memories."

The researchers are now building on this result to try and store light for even longer periods of time (up to a week) in a more energy-efficient way while achieving higher data transfer rates.

In a word of caution, however, Heinze points out that it will probably be several years before this technology is ready for commercial use, and possibly decades before all-photonics devices become the norm in consumer devices.

The team's research appears on the journal Physical Review Letters.

Sources: TU Darmstadt, APS

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion. All articles by Dario Borghino

Thanks for the writeup on this. This is a huge breakthrough.

Zaron Gibson

My question is: how will we eventually go all photonics ? Because the lasers and complex machinery used in this experiment was all electronic. This proves that there are ways to construct and use some optic memory storage devices but not that the environment controlling them could rise to the same rates of energy efficiency and speeds.

Stefan Padureanu


I don't believe this article was suggesting replacing the hardware to run on photons but rather switching the way data is transferred from using electrons to using photons.

However, I'll be your Huckleberry and suggest that eventually we could make that giant leap and switch mostly to photonics over electronics. After all what is a laser (accelerated electrons until they break down into a condensed photon beam). Electrons are more or less the mass equivalent of a photons, which is more an energy particle than mass particle. So then wouldn't it be better to keep energy traveling in a state of energy better than converting it to mass than back to energy. There are already power lines being converted to optical lines (to use condensed light) to transfer electricity/energy from place to place more efficiently. Off course not everything will run on photons but don't forget the processes already running on photons. Doesn't photosynthesis runs on photon energy and isn't it already the largest producer of goods on the planet (plants, food, clothes). You know small things like life as we know it. Think about it.

Matt Fletcher

Getting closer to Bob Shaw's "Light of Other Days"? :)

Stan Sieler

Nothing new here. Superman's been using 'Memory crystals' since the 30's. I believe he keeps a stash at his Arctic pad, Fortress of solitude. It doesn't come with a proper postal address I'm afraid (how very Japanese) ;).

rob simon
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