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An all-optical transistor developed!

Posted: 09 Jul 2013     Print Version  Bookmark and Share

Keywords:Industrial controls  systems  equipment & robotics;Desktop PCs  workstations  servers 

A team of researchers from the Massachusetts Institute of Technology's (MIT) Research Laboratory of Electronics, Harvard University, and the Vienna University of Technology, has described what they call is an experimental realisation of an optical switch that's controlled by a single photon that allows light to control the transmission of light.

It's the optical analogue of a transistor, the fundamental component of a computing circuit, said the researchers.

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 per cent of the light in the signal can get through.

The paired mirrors constitute what’s known as an optical resonator. “If you had just one mirror, all the light would come back,” explained Vladan Vuletić, the Lester Wolfe Professor of Physics at MIT, who led the new work. “When you have two mirrors, something very strange happens.”

Light can be thought of as particles — photons — but it can also be thought of as a wave — an electromagnetic field. Even though, on the particle description, photons are stopped by the first mirror, on the wave description, the electromagnetic field laps into the space between the mirrors. If the distance between the mirrors is precisely calibrated to the wavelength of the light, Vuletić explains, “Basically, a very large field builds up inside the cavity that cancels the field coming back and goes in the forward direction.” In other words, the mirrors become transparent to light of the right wavelength.

In the MIT’s researchers’ experiment, the cavity between the mirrors is filled with a gas of supercooled cesium atoms. Ordinarily, these atoms don’t interfere with the light passing through the mirrors. But if a single “gate photon” is fired into their midst at a different angle, kicking just one electron of one atom into a higher energy state, it changes the physics of the cavity enough that light can no longer pass through it.

Joining Vuletić on the paper are lead author Wenlan Chen and Kristin M. Beck, both PhD students in his group; Robert Bücker of the Vienna University of Technology; and Michael Gullans, Mikhail D. Lukin and Haruka Tanji-Suzuki of Harvard.

For conventional computers, the chief advantage of optical computing would be in power management: As computer chips have more and more transistors crammed onto them, they draw more power and run hotter. Computing with light instead of electricity would address both problems.

Of course, clouds of supercooled atoms are not a practical design for the transistors in, say, a Web server. “For the classical implementation, this is more of a proof-of-principle experiment showing how it could be done,” Vuletić says. “One could imagine implementing a similar device in solid state — for example, using impurity atoms inside an optical fiber or piece of solid.”

Quantum-computing applications may be more compelling. Bizarrely, tiny particles of matter can be in mutually exclusive states simultaneously, something known as superposition. Where a bit in a classical computer can be either on or off, representing 0 or 1, bits built from particles in superposition can represent 0 and 1 at the same time. As a consequence, they could, in principle, evaluate many possible solutions to a computational problem in parallel, rather than considering them one by one.

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