A taut string sounds higher, a slack one lower. A quantum dot in a nanowire is a lot like that string: squeeze it and it glows blue, ease the squeeze and the light turns redder. The trouble is that while nanowires grow, every dot gets squeezed in its own way, so their colors don't match. Quantum networks need all the dots to glow identically.

Scientists have found a way to "tune" each string with a beam of light. A nanowire with a quantum dot is coated with a shell of a special material that softens under light, like wax. When a laser is aimed at the shell, it flows slightly and releases some of the strain on the quantum dot. The light from the dot turns redder. At room temperature the shift is small, but on cooling to 12 K (minus 261 degrees Celsius) it reaches a noticeable size: the color changes by about 30 nanometers, comparable to the width of an entire channel in fiber-optic communications.

What's great about this approach is that the nanowire itself never has to be touched: light works at a distance and very locally. You can tune one dot on a chip without disturbing its neighbors. This brings us closer to quantum networks, where many emitters have to work in concert.