Optical transistor triggered by a single photon

Nature : Thanks to their ability to switch on and off and amplify signals, transistors are a key component of electrical devices. Several projects have demonstrated the possibility of creating transistors that are controlled by photons instead of electrical signals. The most recent, created by Wenlan Chen of MIT and her colleagues, relies on only a single photon to achieve this functionality. The proof-of-concept project uses a cooled cloud of cesium atoms and a principle called electromagnetically induced transparency in which a photon with a specific energy switches the cloud of cesium atoms between excited and ground states. When the atoms are in ground states, they allow light to pass through the cloud. Neither Chen’s transistor nor other optical transistors are likely to replace traditional ones any time soon, however, as the size and energy costs are significantly greater.