The mirror uses a nanoscale optical fiber only 400 nm in diameter to place the chain of cesium atoms in just the right alignment to reflect the light. (For reference, a human hair is roughly 80,000-100,000 nm thick.) Because of the extremely tiny scale, the atom chains had to be precisely spaced at half the wavelength of the light beam -- which also means the color of light had to be specifically chosen.

As Popular Mechanics notes, the team was able to use the mirror to temporarily trap the light beam, essentially creating a sort of optical diode that can store and retrieve light pulses. As Corzo concludes in the paper, this may eventually prove useful in building light-based photonic circuits that will vastly increase computing speeds.