The secure transmission of data is essential in our interconnected society but is constantly at risk as attackers keep seeking vulnerabilities and new methods to decrypt our messages. The emergence of quantum computers adds to the problem, as they hold the potential to break current encryption methods. A response to these threats is offered by quantum key distribution (QKD)—a cryptography technique exploiting the peculiar laws of quantum mechanics. In QKD, two remote users (Alice and Bob) exploit single photons to generate and exchange cryptographic keys with perfect security, as the activity of any eavesdropper would be spotted through changes in the photons’ quantum states. Photon losses, however, limit the speed and distance at which a QKD key can be transmitted, posing a barrier to applications. Some recently demonstrated protocols can in principle overcome these limitations, but at the price of impractically complicated setups. A series of studies, performed by the independent teams of Zhiliang Yuan of the Beijing Academy of Quantum Information and Jan-Wei Pan of the University of Science and Technology of China now shows the possibility of dramatic setup simplifications, removing the need for complex “phase-locking” schemes [1–3]. Yuan’s team’s solution, in particular, removes the need for even tracking the phase of the used lasers. It also achieves secure-key transmission up to 500 km at orders-of-magnitude-larger rates than previous demonstrations, approaching values of practical interest [1]. Together, these advances bode well for the transformation of QKD into a broadly available, commercial technology.
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