Optical computing using light rather than electricity to perform calculations could pay dividends for both conventional computers and quantum computers, largely hypothetical devices that could perform some types of computations exponentially faster than classical computers.

But optical computing requires light particles photons to modify each others behavior, something theyre naturally averse to doing: Two photons that collide in a vacuum simply pass through each other.

In the latest issue of the journal Science, researchers at MITs Research Laboratory of Electronics together with colleagues at Harvard University and the Vienna University of Technology describe the experimental realization of an optical switch thats controlled by a single photon, allowing light to govern the transmission of light. As such, its the optical analog of a transistor, the fundamental component of a computing circuit.

Moreover, since the weird, counterintuitive effects of quantum physics are easier to see in individual particles than in clusters of particles, the ability to use a single photon to flip the switch could make it useful for quantum computing.

The heart of the switch is a pair of highly reflective mirrors. When the switch is on, an optical signal a beam of light can pass through both mirrors. When the switch is off, only about 20 percent of the light in the signal can get through.

The paired mirrors constitute whats known as an optical resonator. If you had just one mirror, all the light would come back, explains Vladan Vuleti

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