  Quantum key distribution (QKD) is a revolutionary cryptography response to
the rapidly growing cyberattacks threat posed by quantum computing. Yet, the
roadblock limiting the vast expanse of secure quantum communication is the
exponential decay of the transmitted quantum signal with the distance. Today's
quantum cryptography is trying to solve this problem by focusing on quantum
repeaters. However, efficient and secure quantum repetition at sufficient
distances is still far beyond modern technology. Here, we shift the paradigm
and build the long-distance security of the QKD upon the quantum foundations of
the Second Law of Thermodynamics and end-to-end physical oversight over the
transmitted optical quantum states. Our approach enables us to realize quantum
states' repetition by optical amplifiers keeping states' wave properties and
phase coherence. The unprecedented secure distance range attainable through our
approach opens the door for the development of scalable quantum-resistant
communication networks of the future.
