Figure 1

QDKD scheme: particle B of an EPR pair $\mid {\psi }_{\text{AB}}^{-}⟩$ is sent from Alice to Bob and backward. Alice’s and Bob’s encoders selecting the local operation on particle (${\mathbf{1}}_{\mathrm{B}}$ or ${\widehat{Z}}_{\mathrm{B}}$) together with the incomplete Bell’s measurement by Alice establish the key. Some pairs are randomly selected for nonlocal measurement (the anticorrelation check performed by spatially separated Alice and Bob measurements), as test of the transmission security. The more general eavesdropping attack is represented by the coupling of the EPR pair with a larger Hilbert space in the initial state $\mid e_{\mathrm{E}}⟩$ by means of unitary operators ${\widehat{J}}_{\text{BE}}$ and ${\widehat{K}}_{\text{BE}}$.Reuse & Permissions

Figure 2

Plots of ${\mathcal{I}}_{\text{B:E}}$ (a) and ${\mathcal{I}}_{\text{A:E}}$ (b) vs $P_{\mathit{corr}}$ and $q$.Reuse & Permissions

Figure 3

QDKD setup: photon pairs are generated by parametric down-conversion in type-II nonlinear crystal (NLC2) pumped by the pulsed laser system (GL, Ti:Sa and NLC1). The bits of the keys are encoded in the phase of the entangled state by means of half-wave plates (HWPs). The incomplete Bell-state measurement is performed with an interferometer analogous to the one used in Ref. 3, consisting of a 50:50 beam splitter (BS), interference filters (IFs), fiber couplers, fibers integrated polarizing beam splitters (PBS), and single-photon detectors. M stands for mirror, DM dichroic mirror, L lens, CC birefringence compensation crystals.Reuse & Permissions

Figure 4

Coincidence rates obtained from pairs of detectors $1\mathrm{h},2\mathrm{v}$ or $1\mathrm{v},2\mathrm{h}$ (open square), and $1\mathrm{h},1\mathrm{v}$ or $2\mathrm{h},2\mathrm{v}$ (circle) vs the displacement of the beam splitter.Reuse & Permissions