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Description
Entangled photon pair sources are essential resources for quantum technological applications. AlGaAs Bragg reflection waveguides are promising platform for such sources due to their high nonlinear coefficient, room temperature operation, and non-birefringent nature [1]. By using a type-II SPDC process, the down-converted photons are orthogonally polarized, and the generated photon pairs are inherently polarization entangled. Here, we present the generation and distribution of polarization-entangled photons over a 28 km dark fiber link. The link consists of commercial fiber, deployed both underground and overhead, includes several patching points, resulting in a transmission loss of $\approx$ 19 dB. The source produces a state with 95.7 $\%$ fidelity and 92.4 $\%$ purity w.r.t. the $|\psi^{+}>$ Bell state. After transmission over the actively stabilized [2] fiber link, the fidelity reduces to 87.9 $\%$ due to residual uncompensated polarization rotation whereas the purity remains unchanged (92 $\%$). In summary, we demonstrate a room-temperature entangled photon pair source at telecom wavelength, suitable for real world quantum applications. [1] F. Appas et al., J. Light. Technol. 40 (2022). [2] S. Kucera et al., npj Quantum Inf. 10, 88 (2024).
