A team of researchers at Princeton University has developed a new method for constructing quantum repeaters using telecom-ready light from a single ion. The study, published in Nature, details the basis for this new approach, which has the potential to revolutionize long-distance quantum communication.
Quantum signals, unlike classical data signals, cannot be amplified over long distances. They must be repeated at intervals using specialized machines called quantum repeaters. These repeaters are crucial for future communication networks that will enhance security and enable connections between remote quantum computers.
The Princeton researchers’ new approach involves sending telecom-ready light emitted from a single ion implanted in a crystal. Unlike other quantum repeater designs that emit light in the visible spectrum, this device uses a single rare earth ion implanted in a host crystal. The ion emits light at an ideal infrared wavelength, eliminating the need for signal conversion and allowing for simpler and more robust networks.
The device consists of a calcium tungstate crystal doped with erbium ions and a nanoscopic piece of silicon etched into a J-shaped channel. The ion emits light up through the crystal, and the silicon piece catches and guides individual photons into a fiber optic cable. Ideally, these photons would be encoded with quantum information from the ion’s spin, allowing for the transmission of quantum states across long distances.
The researchers faced challenges in selecting the optimal material for the device. They worked with hundreds of thousands of candidate materials and eventually settled on calcium tungstate, which hosted single erbium ions with minimal noise. The team built an interferometer to demonstrate the new material’s potential for quantum networks, showing a strong suppression of individual photons, indicating indistinguishability.
While the research represents a significant breakthrough in quantum communication, the team acknowledges the need for further improvements. Specifically, they aim to enhance the storage time of quantum states in the erbium ion’s spin by refining the calcium tungstate and reducing impurities.
The study was supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Co-design Center for Quantum Advantage (C2QA). The team comprised Jeff Thompson, Nathalie de Leon, Robert Cava, Łukasz Dusanowski, Sebastian P. Horvath, Mehmet T. Uysal, Christopher M. Phenicie, Paul Stevenson, Mouktik Raha, Songtao Chen, and Salim Ourari, who co-led the research.
With this new method for constructing quantum repeaters, the future of quantum communication looks promising. As researchers continue to refine the technology, quantum networks may soon become a reality, revolutionizing communication systems and enabling secure and efficient connections between quantum devices.