This demonstration is of great significance since light is the "workhorse" of contemporary communication systems, and single photons are expected to form the backbone of future quantum communication systems
Like fishermen catching a single fish out of a school of fish swimming in a river, scientists at the Weizmann Institute recently succeeded in plucking a single photon from a flash of light.
This demonstration is of great significance since light is the "workhorse" of contemporary communication systems, and single photons are expected to form the backbone of future quantum communication systems. "Contemporary optical communication systems use flashes of light, in which many photons, to represent each bit," says Dr. Barak Dayan, from the Department of Chemical Physics at the Weizmann Institute of Science, who led the research. A bit is a kind of switch that can be in one of two states: zero or one. In contrast, a "quantum bit" can be found simultaneously in any combination of the two states. "Once we move to quantum communication," says Dr. Dayan, "there will be no choice but to use individual photons, each of which represents a 'quantum bit.' Therefore, the ability to control the movement of individual photons arouses great interest, and promotes the possibility of the application of various quantum technologies."
Dr. Dayan and his research group, including Dr. Serge Rosenblum and research student Oral Bechler, built a complex system that makes it possible to "tear off" a single photon on demand. The mechanism they developed relies on a physical result called Raman interaction of a single photon, or SPRINT for short. This mechanism is based on working with a single atom or, alternatively, on an atom-like system. "The advantage of the SPRINT result," says Dr. Dayan, "is expressed in the fact that it is completely passive, that is, it relies solely on the interaction between the atom and the flash of light that hits it." In a previous study, the scientists used the SPRINT result as a switch for individual photons, which allowed them to direct the photons to different paths. In this work, each atom functions as a trap rather than a switch, and it "extracts" a single photon from the stream of photons flocking in their orbit, directs it in a different direction and then turns itself off. The findings of this study were recently published in the scientific journal Nature Photonics.
The experimental system of Dr. Dayan and his research partners relies on a combination of some of the most advanced technologies today: cooling and trapping atoms using a laser (in this case, rubidium atoms), the production of tiny glass devices on a silicon chip, and the production of special optical fibers whose thickness is measured in hundreds of nanometers . "It is possible to harness the ability to deflect a single photon from a photon beam for various purposes," says Dr. Dayan, "starting from basic research to eavesdropping on quantum communication and encryption systems, which rely on single photons."
