Discrete and Process Automation

MIT Researchers "Conceptualize" Single-Photon Switch

08 July 2013

Researchers at MIT’s Research Laboratory of Electronics together with researchers at Harvard University and the Vienna University of Technology have described an experimental optical switch that’s controlled by a single photon, allowing light to govern the transmission of light.

This optical analog of a transistor where a single photon is used to flip the switch could make it useful for quantum computing, according to the researchers.

The switch made of a pair of reflective mirrors works such that 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 what’s known as an optical resonator. “If you had just one mirror, all the light would come back,” explained Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, who led the new work. “When you have two mirrors, the electromagnetic field of light particles laps into the space between the mirrors if the distance between the mirrors is precisely calibrated to the wavelength of the light, Vuletic explained. The mirrors become transparent to light of the right wavelength.

Joining Vuletic 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.

Quantum-computing applications gain from this research. Superposition is much easier to preserve in photons, for exactly the same reason that it’s hard to get photons to interact. The ability to switch an optical gate with a single photon opens the possibility of arrays of optical circuits, all of which are in superposition. It could also help get rid of quantum noise. “Quantum feedback can cancel — to the extent allowed by quantum mechanics — quantum noise,” Vuletic said. “You can make quantum states that you wouldn’t otherwise get.”

The switch could also be used as a photon detector: If a photon has struck the atoms, light won’t pass through the cavity. “That means you have a device that can detect a photon without destroying it,” Vuletic said. “That doesn’t exist today. It would have many applications in quantum information processing.”

MIT researchers’ are confident that the results can be reproduced in physical systems and that are easier to integrate into computer chips.

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