The computing world changed forever when the first electronic transistor was built, as it set us on the path to ever smaller and faster computers. At the time the potential of the technology may have seemed unlimited, but now we are approaching a hard limit in what traditional transistor can do, so researchers are working on new designs. Those at MIT, Harvard University, and the Vienna University of Technology have recently built an all-optical transistor which could lead to a new wave of innovation.
Optical computers have been a goal of researchers for some time, but achieving them is difficult as light does not normally interact with itself and otherwise mechanisms are needed. In this case the mechanism was an optical resonator and cloud of supercold cesium atoms. An optical resonator is simply two mirrors facing each other, so photons will bounce back and forth between them. However, thanks to quantum mechanics, precisely tuned light waves can be made to pass through the mirrors, as though they were transparent. The cloud of atoms between the mirrors will normally not interfere with this process, but if even one electron in the cloud is bumped into a higher energy state, the cloud will become opaque and block much of the light. As the researchers have demonstrated, a single photon is all that is needed to switch the cloud's transition from transparent to opaque, making the device an all-optical transistor.
While the supercold cesium atoms will prevent this transistor design from entering computers anytime soon, it does represent a proof-of-concept for future devices that may. Some of those devices may even be quantum computers, as photons can be used as quantum bits.