Scientists discover a new way to slow speed of light

By controlling its travel at normal room temperature, it could lead to benefits for computers and fiber optics.

For the better part of a decade, scientists have applied brakes to the speed of light. They've slowed light from its breathtaking 186,000 miles a second to mere bicycle speeds, and even "stored" it briefly.

But the experiments often required highly elaborate equipment and exotic materials such as hot or frigid gases to help apply the brakes.

Now, researchers at the University of Rochester, N.Y., say they have slowed light to Indianapolis 500 speeds in specially treated crystals of alexandrite and at room temperature.

The results, they say, could lead to a new generation of components that could be used to build optical and quantum computers and more-efficient optical communications systems.

At this stage, the experiment represents a "proof of principle," says Matthew Bigelow, a member of the research team that is reporting its results in today's edition of the journal Science.

But, he adds, it's not hard to envision applications. For example, over the near term, it might be possible to develop devices that control the flow of "packets" of information pulsing through a fiber-optic network, he explains.

Today, if heavy traffic stifles travel along a particular path in a network, packets are steered into large coils of fiber-optic "delay" lines that hold up the packets' departure until the traffic thins or an alternate route is picked. Those coils, often consisting of fiber-optic lines nearly a mile long, could be replaced by a "slow light" device a few inches long, Mr. Bigelow says.

Practical applications

The Rochester teams' results also highlight a broader quest to find materials and processes that could lead to enormous technological advances if their unique properties could be harnessed at room temperatures. These range from the hunt for room-temperature superconductors, which carry electricity with virtually no losses, to the search for ways to duplicate nature's room-temperature "chemistry factories" to make materials such as spider silk or the adhesives that allow geckos to cling to a ceiling.

Being able to produce processes whose performance peaks at room temperature "simplifies things tremendously," says Jun Ye, a physicist at the National Institute of Standards and Technology lab in Boulder, Colo. "We always want to do things at room temperatures because we live in this room-temperature environment."

Physicists have long known that light can slow while it passes through different materials. Glass, for example, can bring light passing through it down from roughly 100 million miles an hour to a more modest 50 million miles an hour.

But that is still far too fast for optical information processing and storage purposes, particularly for quantum computing, which uses the quantum states of atoms and photons as the "information" bits that represent data, Dr. Ye explains. By slowing light down, "the photons will live longer and any information they carry will be retained longer," he says. In effect, slowing the light slows its dissipation, he adds.

Thus, Ye says, the challenge is to slow light while at the same time preventing it from being absorbed by the material that slows it down.

In 1990, researchers at Texas A&M University hit on a technique known as electromagnetically induced transparency, which uses lasers to tweak the energy states of the atoms in the crystal in such a way as to retain the crystal's transparency while boosting its ability to slow light - its refractive index. They conducted their experiments using a gas.

Last year, a team at MIT reported having used the same approach on a yttrium-based crystal to slow light to around 100 miles an hour. Ultimately, they were able to trap it inside the crystal. But their samples were chilled to a frigid 5 degrees above absolute zero.

Improvement on earlier experiments

In contrast, the Rochester scientists were able to get their intended effect at room temperature and by taking advantage of a different quantum-physics mechanism than the MIT group. In addition to slowing the light, they also were able to speed its passage through the crystal at so-called superluminal speeds - higher than 186,000 miles a second.

Now, Bigelow says, the team is expanding its search for materials that can be used in light-slowing devices and is interested in seeing if they can halt light in the material as well.

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