Photonic quantum computer

Light is made of tiny particles called photons. A photonic quantum computer stores information in properties of a photon, such as which path it takes and which direction it vibrates. It calculates by sending photons around a chip carved with thin channels for light and making them meet each other.

Light is not easily shaken by heat nearby, so the chip itself can usually run at normal temperatures, and it fits well with optical communication technology, which makes it good for linking many machines. But photons are easily lost on the way, and entangling photons is tricky. The detectors that count light one particle at a time often have to be cooled.

If the other approaches hold beads still and work on them, this one is like writing letters on flying table-tennis balls and passing them back and forth to calculate. The key is not to drop the ball.

Investment is flowing into this approach in the hope that it relies less on big refrigerators and can use semiconductor and optical communication factories that already exist. But its success depends on how much the loss of light can be reduced.