Xiaoqing Pan

An ordinary piece of semiconductor weakly changes the color of light passing through it. For decades, physicists worked around this limitation by placing the crystal in clever surroundings, but the material itself remained the same. Now researchers have assembled a "sandwich" of alternating thin layers of gallium arsenide and aluminum gallium arsenide.

A glowing spot in a crystal is like a lighthouse in fog: the longer it shines, the more reliable the signal. In quantum devices, ions of rare-earth metals embedded in a transparent lattice play the role of such a lighthouse. They absorb energy and release it as a flash of light. But if there are atoms with magnetic moments nearby, the flash quickly dies out.

A sheet of paper weighs almost nothing, but stack a hundred sheets and you get a noticeable pile. That's roughly what scientists did with a material that excels at converting one color of light into another, but only when it's just one atom thick. A single layer is like a single sheet: it works beautifully, but it's too thin to produce much light.