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.

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

With the rise of quantum technologies, data security increasingly relies on quantum cryptography and its most notable application, quantum key distribution (QKD). Yet, current technological limitations, in particular, the unavailability of quantum repeaters, cause relatively low key distribution rates in practical QKD implementations. Here, we demonstrate a remarkable improvement in the QKD performance using end-to-end line tomography for the wide class of relevant protocols. Our approach is based on the real-time detection of interventions in the transmission channel, enabling an adaptive response that modifies the QKD setup and post-processing parameters, leading, thereby, to a substantial increase in the key distribution rates. Our findings provide everlastingly secure efficient quantum cryptography deployment potentially overcoming the repeaterless rate-distance limit.

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