A photon is like a car in a multi-story parking lot, where each floor is its frequency (color). Usually it gets stuck on one level, but scientists added an elevator — a programmable modulator that moves the photon between floors on command. This elevator creates links between frequencies, turning them into an artificial lattice, reminiscent of the method of studying light by its frequencies — spectroscopy.
By changing the elevator’s mode, you can get the photon to wander randomly across floors, rhythmically swing up and down, or strictly move only upward with no return. In the experiment, a single photon was born in a superconducting qubit — an artificial atom developed thanks to the discoveries of Bardeen — and raced along a 16-meter cable at nearly the speed of light. The statistics of its jumps obeyed laws studied by Roy Glauber.
The 16-meter cable length isn’t random: it set the spacing between frequency floors at about 10 MHz so they could be resolved and controlled individually.