The world's first photonic router

Weizmann Institute scientists have demonstrated for the first time a photonic router – a quantum device based on a single atom that enables routing of single photons by single photons. This achievement, as reported in Science magazine, is another step toward overcoming the difficulties in building quantum computers.

At the core of the device is an atom that can switch between two states. The state is set just by sending a single particle of light – or photon – from the right or the left via an optical fiber. The atom, in response, then reflects or transmits the next incoming photon accordingly. For example, in one state, a photon coming from the right continues on its path to the left, whereas a photon coming from the left is reflected backwards, causing the atomic state to flip. In this reversed state, the atom lets photons coming from the left continue in the same direction, while any photon coming from the right is reflected backwards, flipping the atomic state back again. This atom-based switch is solely operated by single photons – no additional external fields are required.

"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, including Itay Shomroni, Serge Rosenblum, Yulia Lovsky, Orel Bechler and Gabriel Guendleman of the Chemical Physics Department in the Faculty of Chemistry. The photons are not only the units comprising the flow of information, but also the ones that control the device.