Long-Haul Quantum Key Distribution

Governments and corporations are investing in quantum key distribution (QKD)—a theoretically invulnerable encryption technology—but several barriers still hamper its application. In particular, light attenuation in the optical fibers carrying the quantum signals limits the range over which QKD can work. Recently, researchers have demonstrated an alternative approach—“twin-field” QKD—that could potentially extend QKD’s range by hundreds of kilometers. Its practicality, however, remains questionable. Now, two independent groups, led by Jian-Wei Pan at the University of Science and Technology of China in Shanghai and by Hoi-Kwong Lo at the University of Toronto, have brought the method’s application a step closer by solving a key practical problem.