July 16, 2014

Scientists Devise Photon-based Router

Tiffany Trader
barak dayan illustration

Scientists at the Weizmann Institute say they have developed the world’s first photonic router, an important advance towards building a full-on quantum computer.

The router is a quantum device based on a single atom that can switch between two states. The single atom is coupled to a fiber-coupled, chip-based microresonator. The state is flipped by sending a single particle of light from the right or the left via an optical fiber. In response, the atom reflects or transmits the next incoming photon.

The new development combines laser cooling and the trapping of atoms with chip-based, ultra-high quality miniature optical resonators that couple directly to the optical fibers. These are very advanced technologies and the laboratory responsible for this breakthrough is one of the few with the necessary expertise to carry it out.

“In a sense, the device acts as the photonic equivalent to electronic transistors, which switch electric currents in response to other electric currents,” says Dr. Barak Dayan, head of the Weizmann Institute’s Quantum Optics group. What’s especially interesting is that the switch is operated solely by single photons. The photons comprise the information, and control the device.

It’s the sameness of the control and target photons that makes this scheme compatible with scalable architectures for quantum information processing, as explained further in a writeup in Science Magazine (subscription req’d).

Quantum computing hinges on the phenomenon of superposition, where particles can exist in multiple states simultaneously. Superposition is highly unstable, however and subject to the least bit of interference. Photons are considered to be the most promising candidates for communication between quantum systems because they do not interact with each other at all, and interact very weakly with other particles.

The project represents and important step on the road to more complex quantum-based systems.

Says Dayan: “The road to building quantum computers is still very long, but the device we constructed demonstrates a simple and robust system, which should be applicable to any future architecture of such computers. In the current demonstration a single atom functions as a transistor – or a two-way switch – for photons, but in our future experiments, we hope to expand the kinds of devices that work solely on photons, for example new kinds of quantum memory or logic gates.”

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