MIT Researchers Create Optical Transistor, Shedding Light on Quantum Computing

Optical computing holds enormous potential. In theory, computers could use light rather than electricity to perform calculations which could, in turn, make them speedier. Now, scientists may be one step closer to making this theory a reality. They've described the experimental realization of an optical switch that's controlled by a single photon, allowing light to govern the transmission of light. Essentially, it's the optical analog of a transistor, a fundamental component of a computing circuit.

Optical computing essentially requires light particles, also known as photons, to modify each other's behavior. Unfortunately, photons are naturally averse to doing this. Two photons that collide in a vacuum simply pass through each other rather than interacting.

So how does this new "switch" work? 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. Together, these paired mirrors actually create an optical resonator.

Light can be thought of as particles, but it can also be thought of as a wave--an electromagnetic field. While 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 two mirrors is precisely calibrated to the wavelength of the light, then a very large field builds up inside the cavity. This cancels the field coming back and goes in the forward direction, which means that the mirrors become transparent to light of the right wavelength.

In order to actually create their new switch, the scientists filled the cavity between the mirrors with a gas of supercooled cesium atoms. If a single "gate photon" was fired into these atoms at a different angle, it changed the physics of the cavity enough so that the light could no longer pass through it.

"For the classical implementation, this is more of a proof-of-principle experiment showing how it could be done," said Vladan Vuletic, the lead researcher and a professor at MIT, in a news release. "One could imagine implementing a similar device in solid state-for example, using impurity atoms inside an optical fiber or piece of solid."

While this new technique certainly needs to be refined before it can be used in practical applications, it does show that the method is possible. It also has quantum-computing applications and could be extremely useful in developing new computing systems.

The findings are published in the journal Science.