“You can compare it to shining a laser pointer onto letters mounted on a groove board,” explained Professor Pepijn Pinkse. “The illuminated letter is the information contained in the laser pointer’s light. The number of letters on the groove board determines the amount of information you can transmit with the light.”
The key challenge was to eliminate noise which can impede measurement. To solve this problem, the researchers used a method for detecting individual photons.
The team arranged for the first photon to send a signal to the detector, which then opened. Using a mirror, the second photon was directed at the desired letter of an ‘alphabet’ so that it arrived at the target letter at exactly the same time as the detector opened up. The researchers claim that was the only instant at which photons could pass into the detector. In this way, noise could be eliminated.
It is difficult to specify the maximum amount of information you can transmit with a single photon, according to Prof Pinkse. “Using our method, there is no theoretical limit to the amount of information that can be sent.”