A portable and compact decoy-state QKD sender

Quantum Key Distribution (QKD) enables secure key exchange, based on fundamental laws of quantum mechanics [1] . There exist various protocols which are mathematically proven to be secure, however, for an actual implementation vulnerabilities, due to non-ideal components, must be considered. For example, the usage of faint lasers instead of single-photon sources undermines the security, as even for mean photon numbers per pulse µ ≪ 1 there is a non-vanishing probability of emitting multiple photons. The decoy protocol [2] , [3] offers a countermeasure. When randomly switching between two or more different pulse intensity levels, by exploiting their non-orthogonality, the so-called photon number splitting (PNS) attack can be revealed.