For the first time, researchers were able to build a system in which a single photon could be transmitted while all others were blocked.
The research conducted at MIT is believed to be a milestone in quantum computing as the scientists were able to convert a laser beam into a stream of photons, send it into a cloud of atoms and allow only one photon to emerge on the other side. The achievement is dazzling as photons typically show only weak interactions with atoms. In their research, however, the scientists showed that it is possible for one photon to interact strongly with atoms and change the state of an atom so that it will not allow a second photon to pass through the cloud.
MIT said that the result was achieved by cooling rubidium atoms down to about 40 microkelvins, 40 millionths of a degree above absolute zero (-459.67 degrees F or -273.15 degrees Celsius). In this state, the cloud is opaque and would not allow photons to pass. However, a second laser is uses to facilitate an effect called electromagnetically induced transparency (EIT). A photon that enters via the second laser elevate the atoms to an excited state and pass the cloud at a slow speed. However, a second photon that does not meet the EIT will not be able to pass the cloud.
"So whenever a single photon enters, it passes through the temporarily transparent medium," MIT said. "When two or more enter, the gas becomes opaque again, blocking all but the first photon."
There is the hope that the discovery could lead to the development of a single-photon switch, which could lead to the development of quantum logic gates in quantum computing systems. MIT said that’ such systems "could be immune from eavesdropping when used for communication, and could also allow much more efficient processing of certain kinds of computation tasks."