Tiny Silicon Chip Uses Quantum Physics to Slow Light Down

Scientists have built an optical device smaller than a dime that slows light down to 155 miles per second, the slowest ever managed on a chip.

The tiny silicon chip works at room temperatures and can be mass-produced, with 32 chips on a 4-inch silicon wafer. Previous efforts slowed light to just 0.01 miles per second, but this required a roomful of equipment and temperatures near absolute zero.

Those experiments were “fantastic and very inspiring, but with limited practical applications,” said electrical engineer Holger Schmidt of the University of California, Santa Cruz, who led the study published in November’s Nature Photonics.

Chips based on Schmidt’s work could be used to create all-optical systems that would potentially be “cheaper, faster and use less power,” said physicist John Howell from the University of Rochester, who was not involved in the study. Slowing light on a chip could eventually be used for optical memory, quantum cryptography, and to create simple quantum computers, he said.

Schmidt’s team’s method involves shining a red laser through a tabletop maze of mirrors into the optical chip. The laser, just a few times stronger than a laser pointer, travels through a channel on the chip, and hits a 4-mm-long capillary full of rubidium atoms. As the light smacks into the atoms, they absorb it and don’t let it through.

The scientists then shine another red laser into the rubidium atoms, triggering a quirky quantum mechanical effect that causes the rubidium’s electrons to occupy a different physical state. This turns the previously dense rubidium vapor transparent.

“That was really exciting,” Schmidt said. “Without that second beam, it would be opaque.”

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