We generate pairs of polarization-entangled photons with spontaneous parametric down-conversion (SPDC) process using type-2 non-linear periodically-poled lithium niobate (PPLN) crystal. The SPDC process in the crystal is pumped by a narrow-band CW 780 nm laser, which creates pairs of photons at 1560 nm with orthogonal polarizations. The phase-matching temperature of the crystal is maintained by an oven, which is placed inside the Sagnac interferometer. This setup ensures that the photons exiting the interferometer at the PBS, are entangled in polarization. These photons can then be used for the implementation of quantum communication systems.
Setup
A wide view of the setup we use to produce (left side of the optical table) and measure (right side of the optical table) pairs of entangled photons.
A close-up of the sagnac interferometer with the polarizing beam splitter in the middle and the oven with the PPLN crystal between the two mirrors at the top.
A close-up of the detection/analysis stage.
We detect the single photons using superconducting single photon detectors from Single Quantum. The detectors are positioned in the cryostat (2.4 K) behind the red panel. Below are the electronic drivers for the detectors.
All photos by Marjan Verč.
Projects
Digital Europe Programme (DIGITAL) – SiQUID Slovenian Quantum Communication Infrastructure Demonstration
SiQUID will implement quantum key distribution (QKD) links between multiple government nodes in Slovenia and a test-bed quantum network between research institutions in Ljubljana for advanced quantum-communication protocols. The project will coordinate efforts with public and industrial stakeholders and will train key personnel, young researchers and engineers in quantum technology.
Moreover, the project partners will test advanced quantum communication protocols like measurement-device-independent QKD and the long-distance distribution of entanglement to further increase the security of QKD implementations, and to prepare the ground for a future full-fledged quantum communication network.
The project is in close contact with QCI initiatives in neighbouring countries to facilitate the harmonisation of the national efforts, and to facilitate future cross-border links and the implementation of the space segment of EuroQCI.
Partners:
– University of Ljubljana, FMF (Coordinator)
– Jožef Stefan Institute
– Beyond Semiconductor (Beyond Semiconductor, raziskave in razvoj, d.o.o.)
– Government Information Security Office (Urad Vlade Republike Slovenije za informacijsko varnost)
– Government Office for the Protection of Classified Information (Urad Vlade Republike Slovenije za varovanje tajnih podatkov)