Nicola Laurenti

In practical Quantum Key Distribution, there exist scenarios where the number of exchanged qubits is limited by physical constraints. A notable case is that of satellite QKD, where channel losses and visibility play a major role in limiting the efficiency and the availability of the quantum link. With this perspective in mind, the need for evaluating finite-key effects on the secret key rate is urgent. In this work, we experimentally evaluate, in a realistic setup and with different channel conditions, the robustness of a recent finite-key tight theoretical bound that ensures secrecy against the most general quantum attacks. We compare the experimental results obtained by this bound with the ones achieved with a new finite-key bound tailored for ensuring secrecy against individual attacks. We then show, the minimum number of raw bits to be exchanged in order to obtain a given secret key length, for different values of the QBER. This provides a valuable tool for practical QKD, as it allows to know in advance, depending on the channel noise, how may bits have to be exchanged for obtaining the desired secret key length. The results indicate that viable conditions for effective symmetric, and even one-time-pad, cryptography are achievable.