Cross time-bin photonic entanglement for QKD
Résumé
We report the realization of a fiber-coupled time-bin entangled photon-pair source at 1538 nm. Unlike previous time-bin sources based on type-0 spontaneous parametric down conversion, our approach takes advantage of cross-polarized paired photons generated in a type-II periodically poled lithium niobate waveguide (PPLN/W). We use a fibered birefingent delay line (BDL) in a Michelson configuration to introduce a controllable delay between the paired photons. After the BDL, these photons are separated by a polarizing beam splitter (PBS) at 45° and sent to Alice and Bob. This way we create the non common time-bin entangled Bell state |Ψ+⟩ = 1/√2 [|s,l⟩ − |l,s⟩], where s and l represent the short and long time-bins, respectively.