Balls, beams and quantum computers

by Jane Waite, Queen Mary University of London

Have you played the seaside arcade game where shiny metal balls drops down to ping, ping off little metal pegs and settle in one of a series of channels? After you have fired lots of balls, did you notice a pattern as the silver spheres collect in the channels? A smooth glistening curve of tiny balls forming a dome, a bell curve forms. High scores are harder to get than lower ones. Francis Galton pops up again, but this time as a fellow Victorian trend setter for future computer design.

Francis Galton invented this special combination of row after row of offset pins and narrow receiving channels to demonstrate a statistical theory called normal distribution: the bell curve. Balls are more likely to bounce their way to the centre, distributing themselves in an elegant sweep down to the left and right edges of the board. But instead of ball bearings, Galtan used beans, it was called the bean machine. The point here though is that the machine does a computation - it computes the bell curve.

Skip forward 100 years and 'Boson Samplers', based on Galton's bean machine, are being used to drive forward the next big thing in computer design, quantum computers.

Instead of a beans or silver balls computer scientists fire photons, particles of light through miniscule channels on optical chips. These tiny bundles of energy bounce and collide to create a unique pattern, a distribution though one that a normal digital computer would find hard to calculate. By setting it up in different ways, the patterns that result can correspond to different computations. It is computing answers to different calculations set for it.

Through developing these specialised quantum circuits scientists are bouncing beams of light forwards on the path that will hopefully lead to conventional digital technology being replaced with the next generation of supercomputers.