Researchers create switching device for ‘ultra fast’ quantum internet

According to Prem Kumar, AT&T Professor of Information Technology at the McCormick School of Engineering and Applied Science, the team successfully routed quantum bits, or entangled particles of light, at very high speeds along a shared network of fibre optic cable without losing the entanglement information embedded in the quantum bits. Kumar claims the switch could be used toward achieving a quantum internet where encrypted information would be completely secure, or for networking ultra fast quantum computers. "The device could enable a common transport mechanism, such as the ubiquitous fibre optic infrastructure, to be shared among many users of quantum information," said Prof Kumar. "Such a system could route a quantum bit, such as a photon, to its final destination just like an email is routed across the internet today. "The qubit we're working with is the photon, a particle of light. A photonic quantum network will require switches that don't disturb the physical characteristics (superposition and entanglement properties) of the photons being transmitted. We were able to build an all optical, fibre based switch that does just that while operating at very high speeds." To demonstrate the switch, the researchers first produced pairs of entangled photons using another device developed by Kumar, called an Entangled Photon Source. "We found that if one photon assumed one state, its mate assumed a corresponding one. This held even if the two photons were hundreds of kilometres apart." The researchers then used pairs of polarisation entangled photons emitted into standard telecom grade fibre where one photon of the pair was transmitted through the all optical switch. Using single photon detectors, the researchers found that the quantum state of the pair of photons was not disturbed and the encoded entanglement information was intact. "Quantum communication can achieve things that are not possible with classical communication," said Kumar. "This switch opens new doors for many applications, including distributed quantum processing where nodes of small scale quantum processors are connected via quantum communication links."