Researchers at Weizmann Institute have developed for the first time a photonic router –a quantum device based on a single atom that enables routing of single photons by single photons. According to the reports in Science magazine, this discovery aids in overcoming the difficulties in designing quantum computers.
At the core of the router is an atom that can switch between two states. The state is set by passing 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. In addition to contributing to the flow of information, photons also control the router.
The process involved the combination of two state-of-the-art technologies. One is the laser cooling and trapping of atoms. The other is the fabrication of chip-based, ultra-high quality miniature optical resonators that couple directly to the optical fibers. Dayan’s lab at the Weizmann Institute is well versed in both these technologies.
The idea for creating quantum computers came from the quantum phenomenon of superposition, in which particles can exist in more than one state at once, potentially capable of processing huge amounts of data in parallel. Yet superposition can only last as long as nothing observes or measures the system otherwise it collapses to a single state. Therefore, photons are the most promising candidates for communication between quantum systems as they do not interact with each other at all, and interact very weakly with other particles.
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.”
Source : wis-wander.weizmann.ac.il